If you look at the big picture, there are very few games that benefit much from anything over a basic A1200 - after all most were designed to run on an A500 with maybe a little extra RAM. WHDLoad however adds some overhead and having a bunch of FAST RAM is certainly good, so an accelerator such as the ACA series is a well justified purchase. An MMU is basically not needed for any gaming (I'm sure someone will point out the one or two exceptions there always are
Certain classic games such as Frontier, Settlers, Wing Commander, UFO: Enemy Unknown, most simulation games etc. benefit from more CPU speed and RAM over the basic A1200, so if you play a lot of these, one of the faster models might be useful.
There are of course later 3D games and demos which will benefit from everything up to an 060/PPC/RTG, but I assume these are not what you are mainly interested in?