Aaah holy thread resurrection.....
Just back from a ride on my good old 1996 Mongoose Rockadile SX. I did spend further on it: about 44 quid for a set of Avid Elixirs, 16 quid for a handlebar and $9 quid for a new stem. Another 35 quid for SRAM X5 shifters and I also went for the widest front tyre I could get -a Panaracer Swoop 26x2.4 at 20 quid. So have spent another 124 quid on it. I've spent 310 quid on it during the last four years now, and probably at least another 400 quid on tyres, replacement drivechain, etc prior to that. Now it really is done for upgrades.
But the nicest thing is I'm riding a 24 year old bike and having a ton of fun. Again, theoretically a poor investment (or is it? The cost of the bike new plus 700 quid for 24 years of riding?). The other nice thing is I feel like I really haven't compromized; for the style of riding I do -sedate xc, I have a 9 speed SRAM based drivechain which is supremely smooth, great tyres, dropper seatpost, for me great suspension and one finger braking with excellent power and modulation..... Yeah, I don't have slack geometry, but again I'm doing mild xc, so no problem.