With regards to Nemesis, maybe the ride is aging somewhat poorly with regards to the stress on the track? While the track itself is still glass smooth, I've certainly noticed that a couple of the transitions have become slightly jarring over time (mainly the two corkscrews). They're certainly not jolty to the extent of some of The Smiler's transitions, and they certainly don't stop me enjoying Nemesis, but you can certainly feel them bash you slightly. On the whole, Nemesis is still quite smooth and wows me every time, but I definitely don't think it's the smoothest B&M I've ridden; I actually seem to remember Montu being smoother at Busch Gardens Tampa, and many of B&M's newer coasters tend to have less jarring transitions. Nemesis is still extremely smooth for its age, and it's still a top-notch B&M, in my opinion, but it's certainly not the smoothest coaster I've ever ridden.
To be fair, I'd imagine design technology was less sophisticated back in the early 1990's, so those minor kinks would have been harder to identify in the design. Maybe the park is thinking of retracking Nemesis in a similar manner to what was done to Incredible Hulk at Islands of Adventure in 2016, perhaps with some minor profiling changes to make the ride marginally smoother; we certainly seem to have seen the ride examined a lot more lately, and the crane seems to be coming out more often near the site.