What to do with arcane spellcasting ? (besides casting arcane spells)

[Shadowquad]

Hello Playground,

In an ongoing 3.5 campaign, the DM rewarded our group with magical abilities, for story reasons.
Instead of going for per day Spell-Like Abilities, the DM used the following wording:
"You are able to cast Darkness/Body of the Sun, each one once per day, as a 4th level sorcerer".

So we're all technically able to cast 2nd level arcane spells, at caster level 4 (the DM agrees with that interpretation).

The question is: how can we exploit that ?

Specifically, I'm looking for feats, PrCs, magic items... that have a prerequisite of "arcane caster level X" or "able to cast 2nd level arcane spells", but have another benefit than advancing arcane spellcasting (3 out of 4 PCs don't have arcane spellcasting classes).

I've got very few interesting ideas so far:
- Obtain Familiar > Practised Spellcaster > Improved Familiar
- Divine spellcasters are able to qualify for Geomancer
- Easy access to dual-casting PrCs, none of which seem useful, because there won't be an arcane side to improve.

[Doctor Despair]

You could take God Blooded of Vecna as a level 1 character. Super strong template for avoiding detection.

[Khedrac]

You can use eternal wands - they are a misc magic item that requires arcane spellcasting, but do not require the spell to be on your class spell list.

[Doctor Despair]

As a Primordial Half-Giant (LA +1), you'd have caster level 5, so could go into Sandshaper at level 2, which is neat. You could also go into Blood Magus if you use either a rat familiar (+2 on fort saves) or toad familiar (+3 hitpoints) to gain pseudo-versions of Great Fortitude or Toughness respectively to meet the prerequisites.

If a character has a class feature or special ability that exactly duplicates the effects of a feat, then he or she can use that “virtual feat” as a prerequisite for other feats, as well as prestige classes, and so forth. [...] If the character ever loses the virtual prerequisite, he or she also loses access to any feats or other benefits acquired through its existence. For example, a ranger who wears armor heavier than light loses access to the virtual feats noted above, and thereby to Greater Two-Weapon Fighting as well. Acquiring a virtual feat does not give a character access to its prerequisites.

[Falontani]

Full BAB classes:
Jade Phoenix Mage: Requires 2nd level arcane casting and initiator, advances arcane casting and initiator. You can easily throw a level in a class like Suel Arcanamach to get it's spellcasting progression to add into a JPM build.
Blade Dancer: Requires a caster level. You have that now. Full BAB max speed builds for the win.
3/4 BAB classes:
Daggerspell Mage: Requires CL 5 (easily enough gotten from where you are at) and 1d6 Sneak Attack, 9/10ths arcane progression, some SA progression, its a decent arcane TWF
Acolyte of the Skin: Requires CL 5. I'd stay away from this one if you are a full mage type, but it is... a class...
Enlightened Fist: If one of you was already a monk toss a level into some arcane class, nab Arcane Strike, and then run into the Enlightened Fist.
Green Star Adept: See Acolyte of the Skin.
Rage Mage: Were you a barbarian? Do you want to be a weaker barbarian unless you begin to gish?
Knight of Thorn: I guess? You should have been planning on going Knight of Thorn already if you want to go Knight of Thorn.
Havoc Mage: Become a gish faster, still requires you to grab some sort of casting
Evereskan Tomb Guardian: See Knight of Thorn.
1/2 BAB classes: Are you sure you weren't a spellcaster?
Virtuoso: Did you want to begin to become a bard? Well this isn't the way to do it.
Blood Magus: Early Entry! Caster level 5, 4 skill ranks, 2 garbage feats, and you have to be revived! Good luck with that last one too early, but its a decent caster class if not for the 2 dropped levels of casting. Grants you the interesting scribe scroll and brew potion both before you lose a CL, and a +2 inherent bonus to con before you lose your second one.
Effigy Master: Guess what. This class doesn't require casting. It requires you to have Simulacrum on your spell list (its on the sorc spell list) but doesn't require you to cast it. It requires Craft Wondrous Items, which you meet the prerequisites for. Biggest problem is you need a CL to craft the effigies, and you only have a CL of 4 plus the levels in the class, but if you have a way around CL requirements you can easily drop a single level here for the best benefits of the class.
Mindbender: Want Telepathy?
Master Specialist: Early Entry.
Flux Adept: Skip this. It really isn't worth it. It has a fun combo with Blood Magus, but its a combo that takes 13 levels in the two prestige classes, and really isn't worth it.
Escalation Mage: uhhhhh
Fleshwarper: Requires a familiar. You've already learned the basis of that trick. Its an interesting class and I personally rather enjoy it, but usually on mages. You can combine it with another idea I have below though....
Bonded Summoner: You can do this one. It gives 1/2 spellcasting, which you don't care about, and it gives you a decent companion. I personally prefer High Elemental Binder.
Soulcaster: Were you already an incarnum user? If so you can abandon your normal incarnum stuff for an alternate route! Not terrible, but its really a dual progression and losing out on one side wouldn't be the best.
Sand Shaper: You can do better, but its early entry if you are already a spellcaster
Serpent Slayer: ?
Anima Mage: It probably wont be better if you don't have an arcane caster class to pair with this, but its an alternate progression on the Binder and would work by itself. There are a few spellcasting vestiges that could benefit from the other class features.
Master of Shadow: Basically Bonded Summoner. Its better though.

Special Mentions
Noctumancer. One thing that Mystery users can do better than even spellcasters, is surprisingly, counterspell. They have a few different mysteries that are really good at it. And this class pushes them to be even better. Usually it unfortunately requires you to drop your CL a bit in order to enter, but you can do it without dropping! You can also grab Shadow Familiar + Improved Familiar to boost this further. If you can swing the Heal ranks for Graft Flesh as well, dip into Fleshwarper at later levels. Fleshwarper is good at boosting your familiar, and an Improved Shadow Familiar with the Size Increase can be a terrifying assistant for melee, or if you are using a wand using familiar boosting it

Chameleon. Chameleon does not let you meet prerequisites with most of the features it grants. But with 2nd level arcane casting already, you can progress chameleon's casting (arcane or divine or both) using the 2nd level arcane casting you have for prestige class entry. Chameleon is already a powerful class, and this can make it more powerful.

There are definitely other classes that I missed or left out. There are a lot of classes that you can dip 1 level into any arcane casting class and then use the 2nd level spell to enter into a class and progress your level 1 arcane casting class.

[Shadowquad]

All of those are very useful advice, thank you very much !
To respond an implicit question above, the composition of the group is
- Necromancer Wizard/Fatespinner/Mage of the arcane order (debuff/control)
- Barbarian/Fighter/Frenzied Berserker (ubercharger)
- Cleric / Radiant Servant / Sacred Exorcist (persistomancer)
- Druid (druid)

We are level 13 at the moment, so it's too late for early options -- those are appreciated nonetheless, for theoretical purposes

[sreservoir]

Those spells will qualify you for the Fiery Burst and Shadow Veil reserve feats, though at this level they're probably spectacularly unimpressive.

The cleric might be able to take dweomerkeeper, though the domain requirements (Magic, and probably Knowledge because otherwise Knowledge (arcana) rank is a bit rough) might make that impractical.

The druid might be take arcane hierophant, which progresses the big three druid features losslessly (okay, -1 hp/level) and, uh, gains the benefits of a familiar with basically none of the drawbacks, I guess, but again, might be a bit late to finagle the Knowledge (arcana) ranks. (There is an Argument From Poor Editing that the arcane hierophant, unlike the mystic theurge, doesn't require you to already belong to the arcane class you're progressing (since the requirement is conspicuously missing), but I wouldn't expect that to actually fly.)

It makes the charger a spellcaster and thus capable of crafting alchemical items?

[Kalkra]

Spell Grafts from Dragon #337 can be cool and flavorful, although not particularly powerful compared to early entry cheese.