Instead of buying entire cars for just their wheels, why not let diecast manufacturers sell bags of wheels? Maybe you get 3 pairs for $1. RR’s might be twice the cost. You choose your favorite wheel style, and stock up. No junk bodies, either! Lego does this for individual brick styles. Why not Mattel?
They put out car after car aimed at collectors, and even TH and STH models. One way to promote collecting and customizing would be to offer wheels up for sale. Maybe offer multiple axle lengths too (are there standards, or is every car different?). Why not?
I would love to have a couple Track Day 510's for the steelies alone, but don’t want to stock up on $8 castings (Ebay) that are not really even special without the wheels. I’d also love to snag some more steelies. I’m a steelie-holic.