I'm of the opinion that if it was a good bike in 1997, it's a good bike now. My favorite bike is a 1995 Ritchey, which was still running 7410 8 speed Dura Ace till last fall - I upgraded the brifters and rear derailleur and cogs to 10 speed, because 39 x 25 was getting to be too big. But I kept that beautiful 7410 crankset! Adding more speeds, especially smaller gears, has me back on this bike more and appreciating it all over again, because Tom Ritchey knows how to build bikes. Your Trek looks like a good bike, so unless you're suffering on the hills, I'd keep it as it is. (I might CLEAN it before showing it off here, but otherwise, I'd leave it alone)
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On the other hand, I was bitten by the "Need A New Bike!" bug, and I had the funds and the time to indulge a bit. So I bought a new bike, with carbon frame, disc brakes, semi-compact crank, and 11-34 rear cassette. And I love it!