I don't have a stake in FF so my input is probably of little real value. That said, the testing issue to me would be somewhat secondary to ongoing use.
I guess it's different if running a "pro" schedule across a bunch of tracks and with frequent new cars, but when (if?) I get to race it'll be either SFR or NER, each with a handful of tracks. A bit of testing I'd have a pretty good idea of what I'd want at each. You might have to keep two sets of tires/wheels which is a bit more expensive, but isn't an ongoing expense.