Biggest issue with that bike is the belt drive makes changing the gearing complicated due to the belt not being able to be shortened or lengthened. Just curious,have you had a shop look at you on the bike? If the bars/controls/general fit are off,it could put your wrists at a weird angle that could cause problems. While the cable routing in the Enviolo shifters is a serious PITA,I've found the action to be pretty smooth and not require much effort. If you're having an issue shifting it,your wrists might be at a bad angle or the cables might be mis-routed causing things to bind up.

As for your old bike,when people ask about fixing up old bikes,I ask how much they like it and how well it fits them. If you like the old bike,and it fits well,it might be a good idea to just get it fixed up,providing you don't have to do major surgery. If the BB and headset bearings are shot,the rims are worn or spoke tension a mess,and all the cables need replacing,then it might be time to retire it. If it just needs a tuneup,and maybe some commuting bits like rack and fenders,then you might want to just keep rolling it.