I have a 2004 Trek 1000, and I have had the same "discussion" in my head.

Honestly, if you upgrade the bike's components so it's similar to a higher quality bike... you will be spending about as much as you would pay for a new bike.

On the Trek 1000 you will want to upgrade:
The wheels.
The shifters.
The derailer.
Pretty much all of the components on the back!
Maybe the fork- upgrade the carbon.

Go get a new bike.

The Trek 1000 is a Buick. A solid bike, that's great for a starter bike... but it's always going to be a Buick.

Honestly, you can probably sell it yourself, for almost close to the retail price. I bet you get more if you don't sell it back to the shop. My bike is beat up and old, and I can sell it for $300 (I found a buyer), and I paid $600 for it 2 years ago.

My *dream* is a Specialized Tarmac Elite. At $2,200 (on sale!) it's way out of my price range right now. So, the Trek 1000 stays around. My second bike will be a bike that I LOVE.

Otherwise, I have a new tri bike that I've only ridden around 100 miles. It's a sweet ride, and I will probably be on it most of this year.

Unfortunately, riding a tri bike takes me out of groups rides. Thus, I need a spiffy new road bike!

Good luck with your decision! But I say, go buy what you LOVE the 2nd time around... if you can afford it.