Originally Posted by
jbosh
I can put 50 miles on it and it feels good.
I think that sums it up. As others have said, ride it. Get your money's worth. I suspect the wheels and tires will probably be the first to go - not a certainty, but a strong possibility if you ride it frequently. It looks like those Tiagra calipers may have enough reach that you could fit some 700c wheels on there if need be. You only need an extra 4mm of reach front and back to fit 700c rims. If the time comes that you need wheels, I'd go for a decent set of modern (i.e. 130mm rear hub) 700c wheels. I suspect your rear dropout spacing is 126, so it should be no problem to simply spread the drops manually to fit a 130mm rear hub. You can always take them with you, and if you get a nice set, they will likely be better than anything you can find on a modern LBS $700 road bike.
Don't feel too bad about upgrading parts, because as long as they are not proprietary (like a French threaded bottom bracket or headset) you can always use them to build up a different frameset.
As for the neck and back pain, +1 on what carpediemracing suggests - it could simply be normal soreness. However, you may find you are too crowded and need a longer stem, or (as is my case) you need to raise the stem to alleviate neck pain.