Even so, Poly Other is a great attack spell. And, it can be used as a buff spell in a pinch (although I think it's pretty cheesy). I've never run a character who used enervation but it looks great on paper. -1d4 to everything (attacks, saves, damage, etc.) and lose the highest 1d4 spells prepared and if you're up against a levelled villain, you can kill them with a few of them as well. On average, a level ten villain will go down to four enervations. Improved Invisibility would help make up for your AC and it would be a good buff for the party's rogues. Putting it on the party's fighters might not be such a hot idea though since the bad guys would they can't do their job as meatshields as well if they're invisible.
Alternately, you might want to take Confusion. It's really good for large numbers of low will save baddies.
So, if not Evard's Black Tentacles, I'd take one of the following:
Polymorph other, Confusion, Enervation, Improved Invisibility.