I have bought pretty much only standards for a few reasons:
1 Budget. The game is tight enough on Cr I have to manage funds to keep things moving
2 Prize cars. I hate buying a car only to have it prized to me later on... I would REALLY hate this if it were a premium... cost thing again.
3 Wider variety. When I need to fill a spot to enter a race, shopping the used cars gives me more options and thus usually cheaper (even ignoring they are used) options.
This is unfortuante becaues I don't like the bumper cam view of standards... I really like the cockpit and going to bumper cam I loose sense of my cars space and also the ability to see who's around me via mirrors.
So much for just not using them if I don't like them... it's one have dozen or the other: the game is very hard to continue due to money issues if I buy premium or I have to buy standards