Im also in the camp that wouldnt touch this bike other than maintenance needed just to keep it rolling
i outlined my experience riding a 15 year old Santa Cruz in Bentonville just now on prj71’s post about “budget mountain bikes” - i wont re-write it, but id think for $500 + or - you could find something like that to keep up with your buddies.
After all, we all know that aluminum frames and 26” wheels are worthless for real trails (wink - nudge - im kidding , but they dont hold much resale value so you can find them periodically for attractive prices- ).
but thinking about a fork upgrade for you — lets see, $250 fork, $30 headset, $80 for new stem and bars, - thats $360 in parts by itself conservatively.
andis the bike labelled a “Fisher” or a “Gary Fisher” ? Thats an important distinction because Fisher was bought out by Trek at some point and started calling allhis bikes Gary Fisher . (I could have the name thing backwards) but the older pre Trek buyout Fisher’s are classics, along the lines of a real Ritchey, Bontrager, Yeti etc. and if yours is one of those, i wouldnt touch it with a 10 foot pole(except for replacing consumables , tires, cables, etc )
but as always, just giving my thoughts based on my experiences , andd with your bike and experiences - its your rules
have fun