Should I upgrade my 50D?

I have a 50D that I am perfectly happy with. I've been thinking if I should upgrade to either the 60D or 7D, keeping in mind the resale value of the 50D. Right now, it has a good resale value.

Should I just hold on to the 50D until it dies? I don't need to shoot video and not sure how much better pics will be with the new sensor. The 63 zone metering sounds good, as I find the one on the 50D lacking sometimes in challenging situations. High ISO is not that important to me since I shoot with my 17-55 f/2.8 in low light anyway, and have never been unhappy with the 50D's performance at ISO 800 or so. For even more challenging situations, I use my 50 f/1.4.

On the other hand, I think the 50D will not have much of a resale value 2 years from now, and would have to spend full list amount to get the latest and greatest.

Any opinions? Do I just have upgraditis