Why do you say this, out of interest? While I've personally found Nemesis to have gotten slightly joltier in some of the transitions within the last year or two (the corkscrews and zero-g roll in particular definitely bashed my ears a bit last year), and this has made me rank it slightly lower than I used to, it's still pretty smooth for a coaster of its age and doesn't really vibrate noticeably against the track or bash your head about at all. Compared to Infusion at Blackpool, it feels like gliding on air!
Bits of the track have already been replaced as far as I'm aware, and surely in a time where the park will be wanting to be a little more careful with money post-Covid, a new ride (SW9) would make more sense and have a greater chance of financial returns than a major refurbishment of Nemesis, which isn't really needed at the moment, in my opinion.
If they were to do one, though, I think it would be nice if we saw some of the inversions smoothed out a bit; maybe the corkscrews and zero-g roll could be smoothed out a bit?