"It's stupid to spend a few hundred bucks upgrading this bike. Instead you should spend $1500 on a new bike."

Huh? For what it's worth, 26" rim brake is my preferred MTB type. Yes, I've ridden and owned most of the other kinds.

All the usual suspects have been mentioned. Personally I think a vintage Rock Shox would fit this bike best. Lighter than the new forks available and also with the least amount of travel, so you change the front end the least. Finding one in good shape is the challenge.

I still need to try that new (but now already discontinued...) Rock Shox silver fork. Even though it's on the heavy side, the price is right and we may never see another new 26" rim brake fork again.