Only first place is good enough for me, I've completed all books, nearly all missions (some of the bugged tire ones, but not all) collected 161 cars so far and my collector exp is 68,900.
I have gotten 0 engine swaps so far. Did get ferrari and aston martin invites, and have gotten a not-for-sale engine bore upgrade for the BAC Mono plus the Ultra-high rpm turbo for the Veyron (which I haven't been invited to buy yet, sadly).
I don't think it matters. At one point I thought maybe my collectors level would deliver me some higher star roulette tickets, but that also hasn't been the case at all.