I was hunting for this kind of info before I bought my 2003. I don't think there is anything inherently wrong with the bikes, other than the tank issue mentioned above. My interpretation of online info has been that the SP2 is a "better" version to buy...but not lightyears beyond the SP1.
Like Evolved said...just look out for a bike in good condition with decent milage at a good price. Heck, I'd pay a little more for a well maintained bike. Also, interview the sellers...that will tell you a lot about how the bike was treated.
Bike: 2003 RC51
Car: 2008 Lancer Evo X GSR
Truck: 2001 Nissan Frontier