Daggerspell Secret Agent (Help!)

[Roguenewb]

So, I've decided that I want to play a *fixer* type character. A guy who's really good at getting past defenses and recovering information or making a single telling strike. A field agent/infiltrator type character. To pull this off, I decided to go with this general build, help is appreciated, especially because at the moment, I have a small shortness on Search Ranks.

Magic Blooded Human

Trickster Spellthief 1-5
1.) Able Learner
H.) TWF
Flaw.) Weapon Focus Dagger
Flaw.) Craven

3.) Weapon Finesse

Daggerspell Mage 1 (Swapping all the relevant skills through Cityscape)
6.) Acidic Splatter (??)

Unseen Seer 1-2
Extra spell (Hunter's Eye)

Daggerspell Mage 2-10
9.) Arcane Strike
12.)???
15.)???
Unseen Seer 3-5
18.) Practiced Spellcaster

What else do I do for this kind of build?

[Waker]

Going the trickster route loses you a lot of the special abilities that would make you a better infiltrator, like trapfinding and many of your stealth skills. You can make it up a bit with the PrCs, but overall you will still be a weak spellcaster.
A slightly different build would be
Spellthief 1/Combat Wizard 5/Daggerspell Mage 1/Unseen Seer 2/Daggerspell X/Unseen Seer X
Going this route will let you snag Master Spellthief from CScou to make you able to steal higher level spells. You also have a much better spell list to choose from, as well as higher level spells. Combat Wizard was used just to grab extra feats, but you could instead replace that with Spontaneous Divination since you seem to like being aware of your surroundings, also it goes very well with Unseen Seer. At higher levels you could also take levels of Arcane Trickster.

[Roguenewb]

He's sneaking into houses, not dungeons. I prefer spont and I'm avoiding wizard here because I'm trying to balance against a tier 3/4 party