It depends. In general, when you are in the sub $1,000 bike category that came with anything less than Shimano 105, or perhaps Ultegra, what your bike shop says is true. But that is only a generality. If it is a frame that you are absolutly crazy about, then it is worth it, regardless of the bike's street value.

The fact of the matter is you can get some pretty sweet deals on new bikes already built up with the warranty for not much more than a groupo. I've seen some pretty nice Ultegra equiped bikes in bike shops for less than $2000.

If you were to upgrade the bike to say Ultegra (for sake of argument) you are going to shell out over $1,000 for the groupo, not including installation. Since it takes half a day to install a groupo, it is going to get pricey.

Now if you were to be riding say a Cervelo R3 or Orbea Orca or other higher end road frame and needed to replace the groupo, that is a different story. Since those frames alone cost over $2000 each and they probably have really nice wheels too, you would be hard pressed to replace it with a whole bike for about the same as the groupo.

There is also the issue of whether you can do the work yourself. If you are competant with bike mechanics and fine tuning plus own the tools, you can certainly save some dough, but it will take plenty of time to do the swap. And sometimes, you run into issues, which can cost you even more money than you expected. I just changed out my wifes groupo due to a race crash, and it took me a good 6 hours to finish. Its the little details that take so long.

Bottom line: I agree with the bike shop. Go for the whole bike upgrade. There's nothing that I would jump up and down about for a Trek 1000SL. In the end, you'll have a new sweet ride with full warranty.

IMHO, IF (a big if) you did happen to decide on the groupo upgrade, I would not put anything more than Shimano 105 on the 1000SL. The only reason to to go above 105 on such a frame is that you are REALLY after crisper shifting under full load because you race. Groupo weight is a non-issue on the 1000SL. Anything higher than the 105 is just throwing money away.

FYI: I do race on high end frames and still only run Ultegra components. Going to Dura Ace won't make me any faster or more competitive. I put the saved money where it makes a difference. Would I like the Dura Ace. OH YEAH. Who doesn't like the bling factor?

Your shop mentioned lighter frames. Light is good. Very good. We all want a light bike. Just remember that if your goal is to go fast, Aero trumps weight every time, unless you are a 140 lb elite racer who climbs more than 50% of the time. So if you have the option of the trade-off of aero or wieght, go for aero.