Unless you plan to race it, or are restricted to that
size of a bike for some reason, I'd say don't waste your
Take the money you have to spend on extras, and the money
from selling the 500, and buy something bigger.
If you wanna race it, start with exhaust, air filters,
jet kit, heads, cams, etc.
You could dump lots into it.
But is it really worth it?
A jet kit might pick up a few hp...no one makes a lot of performance parts for the 500's, cause the market isn't big enough. Plus, most parts give you a percentage increase in HP...so if you only have 60-70hp to start with, you're not going to be able to boost the power much without MAJOR upgrades. (i.e., turbos, NOS, etc, which cost more than the bike..)
Meddle not in the affairs of Dragons, for you are crunchy and good with ketchup
live with it, you can still go plenty fast...it'll just be a dog on the straights...it's alright though you can improve your corner ability and your technique for clutching up wheelies. it's possible if you become really in tune with your machine.
If I had a penny for every time I've heard this kind of question....
It seems that some people are under the impression that some bikes have a secret way to increase power. But unfortunately, all bike are created using the same principal. There are no secrets in adding more power to your 500. Basically all you can do has been discussed in the replies above. And you also knew ahead of time that the obvious answer would be "buy a bigger bike". Which would have been my suggestion, since now 600 and maybe even 750 weigh as much as your 500 with almost twice the power (potentially). Also, look into getting a used one for $4-$5k. If you dump it, it won't hurt as much.