I beg to differ about the utility of AC however. I understand that TWF is strictly weaker than power-attacking with a two-handed weapon, but AC remains absolutely crucial; each point makes a large difference in the amount of damage you take. Maybe at really high levels an AC increase is less relevant, but actually I don't believe it. I would never ban animated shields, because they harm players who are mostly behind the power curve anyway - fighter types. Beyond that, an animated shield is not the only means of getting shield bonuses - a bucker with improved buckler defense works just as well, and there are rings of shield too.
In any case, all that this means is that a two handed wielder will do more damage than a S+B, and have 2 AC less. I don't see the problem in that. Yes, a S+B-er is less powerful, but it's also even less feat dependant. And at low levels, there just isn't a problem at all - there's no way an animated shield is worth it until at least mid-levels (say 10-11). Power attack is not too powerful compared to cleric's, druids, wizards or sorcerers. It's a powerful alternative at high levels, and perhaps the 2 to 1 scaling is too good, but that's about all.
So if you want to fix PA, then simply make the scaling 1 to 1, but leave the AC's as is. Removing something like animated shields nerf's TWF as well, a style which is sub-par already. Sure, Sword+Board is less attractive, but it's also the easiest to master (as in, at low levels the most attractive).