Just get it working and ride it. Don't be putting money into swapping working old for new. Once you have a ridden it for a few thousand miles then you'll have a better idea what you like and don't like about that bike.
I had a Schwinn Suburban when I was a kid. I think the frame is still at my father-in-laws barn rusting away. Nice bike for leisurely riding and maybe short commutes. Heavy though, so not sure I'd want to go bikepacking with it unless I was still a very young teen or everywhere I want to go has no hills in between.
Modern parts won't boost performance. They'll just work better. The motor is what give you better performance, but the motor doesn't work as well on hills with a heavy bike as it does a lighter bike.