I've not come across an AGA game that ran at a higher resolution than its ECS counterpart. Remember that most of the games were written to be playable on the domestic TV-set.
However... if you can get an A1200 for a box of beer or a nice bouquet of flowers (or just at a tempting price) there's nothing to loose. Afterall there's loads of ways you can still run the old games on it and it gives access to nice upgrades.
For me, Pinball Illusions was a reason to start bidding on an A4000T a few years ago (actually, that's 6 years ago)... which I won. :-)
