I play it ever so often. Never did online play or trading at all just played through getting everything thing to Class S (isn't that hard). Got I think about 100 cars or so, went through the driving challenges to see what ones I could get more credits out of and then eventually just did Test Course runs for credits, see what else in the dealerships would cycle. Don't play it that much due to battery life/dealership cycles/credit grinding over and over.
Beware of playing on another PSP as swapping memory cards gives a 'delete your save' message so don't do that if you want to reset your progress (Sony stopping hacking/save file editors I guess due to PSP encryption being weak).
I'm on a replay-through as was curious about the message and how far it goes with my regular save. since I swapped PSPs (wanted to use my 2000 model for TV out and just realised it says that when you put a memory card into a different PSP than the one you played it with).
