Yeah, I think DA and everyone else expressing similar ideas has it right.
However, that's only to a certain point (but even that could be argued)...
For example, BobK's stated reason is something I agree with as well but if you "need" to get those 200pt races done then buying a slower car is something you need to do (which would mean BobK's reason falls inline with DA's reason for buying cars).
That said, I believe my reason may as well fall under the DA rule... I've got to collect every car in the game.
Ok, maybe not every last car, but I do have a ton and at this point, when I buy a car it is for one of a few reasons...
The Color- If I have a Supra in red but want one in white, I've got to buy another.
The Rarity- If the SS Trueno only comes up every so often, I may want to buy a second car so one can be tuned and the other can remain stock (all the while, avoiding the troubles of not being able to find one when I need it).
The Unique Value- This is the most important issue for my car buying since I managed to buy most of what I wanted. Simply picking a car to drive for personal reasons is often the most rewarding reason for buying a car.
Much like DA's RUFs, many of my cars are picked because I wanted to drive them instead of something else. The RUFs are a great example because you don't actually need to buy one yet most of us want to drive the Porsche replacement.
Likewise, my SLR, Amuse R1, TRD Celica, and '92 NSX R are all purchases for pleasure and nothing else. 👍
So, in closing...
I buy what I need but I need what I want.
