Good advice, I have a Uni filter and Dynojet jet kit on mine, and it has made a noticeable difference. I think it will take a lot more than bolt on stuff to get 10 hp, but 5 should be easy enough with a pipe mod, jet kit, air filter, and vented air box. I've been wanting to get a clutch kit for mine, but EPI dosent make one for the '11 yet. That will be the key though, transferring the power to the ground with a good clutching system.Jet Kit, Air Filter, Clutch Kit, and a slip on. that should put you right around the $500 mark and give you a noticeable power increase. If you dont want to go the slip-on route theres a nice thread on this site about modding the stock muffler on an 800, should be the same procedure for a 500 and will save you $200. Either way you cant go wrong. Check out Hotseat, they seem to have decent prices and nicely setup kits.
When I get the cash this is my plan:
DynoJet Stage 1
Heelclicker Clutch Kit