I would tend to agree this isn't worth it at all. Look around at all the threads about "is President's Circle Worth It?"

I think about 10% of the time I'm happy with my rental as a PC member, so 5*? It's pretty unlucky you're going to get a car that is interesting.

I've found that your best bet for upgrades is just going in and asking how much it would cost to upgrade to X, and have them give you some options and then haggle on the one you want.