I wouldn't alter your GF. I won't list the link to a bike for sale(against BF rules), but a new fork isn't cheap, at least compared to a listing (Louisville, KY) on Craigslist for a Spec.Stumpjumper hardtail--in case you'd want to look just to compare a complete used bike price to a new fork. And no, it isn't my bike-haven't even seen it in person.
PS-my mtn bike started life as a '96 GT hardtail, frame was replaced under warranty in '98, at which time I began upgrades--finished around '05 or so). Nothing left of the orig bike. If I had an older mtn bike now (make that another old mtn bike!), would I upgrade-no, I'd buy a later, used model with more updated parts already on it. And I really like that GF-wouldn't change a thing!