You'll find out quickly that 32 note poly is pretty limited once you start going into recording your work, and layering voices while using styles. 32 notes can go pretty quickly. So having 64 or 96 note poly would be better.

If you're just learning to play and getting into arrangers as well, then the 32 note poly may not be an issue for you yet. Are you going to use the S-500 as a "learning" board to eventually step up to a model with more features in the future? Once you start to get into the board more as you playing skill increases you'll start doing more with the keyboard. As you progress you'll eventually run into the limits of the 32 note poly.