I've got a 1997 Trek 1220 that I picked up relatively cheaply. When purchased, it was freshly tuned with new cables brake pads, chain, cassette, and also with a new wheelset. The cassette had been upgraded to an 8spd (11-27) from the original 7. The STI shifters were gone ... replaced with (ick) stem shifters ... the one thing I really don't like.
Since then, I've ridden it about 2k miles, replaced the cassette and chain once, and went to some larger chainrings. The front triple was 26/36/46 stock. I found I was often riding on "the bottom of the cassette" so went to 26/38/52 and am very happy with those ratios.
So my question is this ... do I continue upgrading this bike? It's a pretty good fit and the frame seems to be in great shape. I'd like to add a set of "brifters" (seems I can find some sora or claris ones for < $50-$60), and possibly upgrade the wheelset (there's some reasonably priced aero-style weinmans out there). Also thinking about a carbon fork ... Nashbar has a 1" carbon fork also for around $100 when on sale.
For just a little more money, I think I'll have all the componentry I'd like to have. But would it be better to just buy a new bike? My price range for a new ride would ideally be < $1000. What would I "gain" going to a new bike that I don't get by continuing to upgrade this one?
I have a ~28-mile round-trip commute that I ride 2-4x per week ... averaging around 17mph. I take longer weekend rides (40-60 miles is typical) and occasionally participate in longer charity rides.