Summon Monster I and Polymorph any object: all that's needed for summons?

[Skaven]

I know, it takes two rounds but as long as you have time to prepare with this setup is there any need for any higher level summon spells? (sans summoning multiples)

I mean, what with the duration of summon spells being so short, the durations on PaO are irrelevant, but you could summon something weak with the SM1 and then transform it into a balor or ten headed hydra or whatever and have it under your command with an 8th level spell for 1 round/level (maybe extended?). Sure it won't get the Su abilities etc but hey, something like a ten headed Hydra could be very worth it as a summons.

Is there something i'm missing with this setup? Is it feasible?

[Urpriest]

Once you've got 8th level spells you can get loyal minions to PaO with arguably fewer resources. Also, at that level the main use of the Summon Monster spells is for SLAs and SU abilities anyway.

[ShneekeyTheLost]

I know, it takes two rounds but as long as you have time to prepare with this setup is there any need for any higher level summon spells? (sans summoning multiples)

I mean, what with the duration of summon spells being so short, the durations on PaO are irrelevant, but you could summon something weak with the SM1 and then transform it into a balor or ten headed hydra or whatever and have it under your command with an 8th level spell for 1 round/level (maybe extended?). Sure it won't get the Su abilities etc but hey, something like a ten headed Hydra could be very worth it as a summons.

Is there something i'm missing with this setup? Is it feasible?

By the time you hit PaO, and are willing to do such things, Planar Ally shenanigans have already been on the table for quite some time. This is a poor use of an 8th level spell slot.

[Randomguy]

Polymorph any object is one of the more broken spells out there.

Why bother summoning something? Turn a pebble or an ally into a solar.

[Tvtyrant]

This makes me wonder if you can PaO your familiar? That would make share spell all the sweeter.

Edit: Yes, yes you can. And the shrew to manticore example means it will usually be quasi-permanent. :D

[ericgrau]

Hit points, BAB and other such things found in the extremely long polymorph rules. Although I always found it amusing that one could summon a fearsome balor that could be taken down with a crossbow bolt and can't hit squat.

The other thing is that it takes 2 rounds which is a long time that you don't always get. I'd rather target a nearby boulder or etc.

Finally the HD cap is another bottleneck of the power of the spell. Between that and everything else you have to weigh it against the power of your other options.