I'm not saying it can't be done. I'm just saying a lot of people used to slapping on a few parts to get some extra power have tried to do the same on the EX500. A lot of them end up spending a lot of time on it and never get it working all that well. You obviously know more about this stuff than I do. I'm just sharing what I've seen over on the 500 forum with people trying (usually unsuccessfully) to get more power out of it.
Here's a dyno of a stock 500 just for a rough idea of what you should be getting out of it.
In
FOG's personal testing, he got 49-51hp stock at the wheel, 52-53 with a pipe and jet kit, and 53.9 with the airbox mod, everything else stock in perfect tune (fresh valve job and cams degreed to ensure factory specs).