Yeah, if its stock then upgrading would effecively break it's best features. Games that run on A500s generally don't take well to speedups. The only add-ons I would recommend would be a harddisk that plugs into the side and extra memory mounted in the trapdoor underneath.
If its unopenned and has Kickstart 2 it may be an A500+, rather than an A500; in which case be sure to pop the case open and remove the battery from the main circuitboard (they leak and destroy other parts, and arn't needed for it to work right).
