It’s been a while but I think I also struggled to hit a solid 60 without substantial graphical downgrades. The biggest thing to check, if they haven’t fixed it, is if you’re using proton? The Linux version of the game, at least as of last year, is total crap. Running the Windows version through proton is a substantial improvement. Hopefully enough to get you to 60fps.
Outside of the major changes of the screen and battery, there’s minor changes in pretty much every area of the OLED. Whether that’s worth it depends. For me, the Deck was my main device, and for that it was completely worth selling the old model and upgrading. If it won’t be your primary gaming device or it will almost always be docked (so not benefiting from the screen or battery), then maybe not. In either case, the power is basically identical and some software changes have been made to massively improve the LCD screen, so you really can’t go wrong.