There certainly is a place for spec racing. I can't argue against it completely or call it useless. But, proper spec racing is a focus on the drivers and not so called manufacturers or constructors. Look at it this way. Really, Chevy and Ford and so forth aren't accomplishing much of anything, beyond marketing, in NASCAR. They're not participating, per se. They're gaining some marketing. They're not gaining any of the technical benefits you can get from innovative racing.
You look at a company like Williams in F1 and they've gotten so much technical skill and low volume manufacturing ability that trickles into the automotive industry, not to mention other high tech applications, particularly in the UK. They even made all the batteries for Formula E for the first seasons of that series, which, as much as I hate to admit it, has actually attracted a lot of OEM interest. Williams is now considered a low budget team, and that's with a budget over twenty times what a NASCAR team has.
GT3 seems to have become what NASCAR was, albeit mostly in Europe. They are closer to "stock cars" by the definition. To be a GT3 car, it has to be available at a dealership, provided one has the money to purchase the thing; after all, they aren't Impalas or Ford Five Hundreds. They are 911s and so forth. But, they're real cars.
Someone once said here that no one would pay to watch things like a Camry or a Ford Five Hundred race. I agree with that. So, the OEMs involved shouldn't pretend that's what's happening. At least in Europe, if you're racing a Golf on the Ring, you're racing a Golf on the ring, not a creation superficially resembling a Golf.
I'm not saying NASCAR should spend itself to death. To the contrary, they should not. However, it's hard to root for a Chevy chassis or engine when that's only a fiction.
As for pay drivers, I'm not sure what the answer is, aside from people continuing to be hobbyists. Just about every form of racing for years has relied on pay drivers of one sort or another.