Goes without saying that no single title is worth buying a whole system for, but Gran Turismo is one of those that had a lot of sway when it comes to a decision like, 'should I upgrade'
However, while the focus is on ray tracing and 8K, that's never been my personal issue with GT7. At no point have I thought, 'wow, this game is ugly'.
Sure, there has been frame rates issues at certain tracks, but there's currently no suggestion that these will be addressed. I imagine it would only get worse while chasing things like ray tracing (it's not like you can turn off ray tracing in certain sections of the lap)
I've said for a while now, the game needs content (heck, I'd take the content they promised us a few years ago at this point) which as you would imagine, is not dependent on which PlayStation you're playing on...