I've spent most of my time on new games simply because it satiates my crave for new experiences even if with long running series, it goes back to what you know + the new added aspects. I do replay games I effectively found immensely enjoyable though.
Also since our brains tend to forget a lot of the dinner details of most experiences with them. Having a new playthrough a few years into the future is also beneficial if you want it.
Best example, Xenoblade Chronicles X, played it 3 times on my WiiU got much further in my last attempt but I didn't finish it. Now we've got the Definitive Edition and despite all the new bells and whistles, it shouldn't technically be as rewarding as it is actually to me right now. I immensely enjoy my time with it.
Nonetheless, going through new games and experiences on the next Switch will likely be just as enjoyable as was the enjoyment I had of playing my Switch in 2017, though for different reasons this time.