You sound like me a couple of months ago. I have a 1994 Chromoly GT Aggressor, 18 speeds, Alivio in the back and Acera in front, single wall rims and no suspension fork. I was also planning to upgrade it but everywhere I asked, the answer from the salesmen at the bike shops was the same: It's just not worth it.

It certainly wasn't. I needed to invest at least 300 dollars and in the end I was getting the same old and heavy 150 dollars bike. For that reason I got a new mountain bike.

What I did with the old one was adapt it with road slicks, fenders and a rack for commuting because I also love my old GT very dearly.

Hope this helps,

Ricardo