I would keep it legal and track it, these bikes are a blast on the street.
Currently I have over 10k on the clock on a 450r(04)that I use as a daily driver. To maintain these bikes you have to be quite religious on air filter changes(once a week)and oil changes(engine side once a week, trans side every other).
Picture is current from today, we had about ~10.16cm of rain in one night. Makes for a wet ride.
Mine is a '02 and the guy I bought the bike from made her into one hell of a track bike and a blast on the street.
Here's the list of performance mods that I can think of.
JE 12.5:1 high compression piston
Custom Web 208 cam
Kibblewhite stainless valves
Ron Hamp bored carburetor with venturi
Yoshimura full titanium TRS exhaust
Uni air filter in vented airbox
Baja Designs wide ratio transmission