I don't know.. In your situation, I think I would go with a new body. Yes, the 20D is still an excellent camera. But I think 7D is a worthy upgrade. Nothing in the 30D, 40D, 50D was a huge "leap" in features and advancement to your 20D, so you've held out.
Granted it's way too early to tell, but IMO, 7D will become a classic. Yes, future cameras will easily break the 20-30mp barrier (as the trend continue to go), but 5184x3456 of the 18mp sensor is a HUGE photo to work with. It'll be plenty sufficient for 20x30 prints easy, for the next 5-25 years.
At 100%, the ISO noise may not be dramatically better (but certainly an improvement), but when viewing the entire photo, you will likely at least see 1 if not 2 stops improvement on the noise itself. I used to only stay at or below iso 800 indoors with my 40D and was very reluctant to go 1600. I don't even give it a 2nd thought shooting 1600 and 3200 indoors now. I haven't shot much 6400 because I haven't felt the need to yet, but I'm glad it's there for the extra stop when I absolutely, desperately need it.
It's true, that glass hold value much better and faster glass can stop action more effectively. But if you're managing okay with f/4, getting 1/500s and shooting 1600. I would imagine you would have no problems getting better results at 1600 or 3200. Just some food for thought.
(Besides, the way you keep your cameras, I suspect the next "upgrade" you do will be the 7Dm3 or m4. Or go full frame by then, which is likely many years out.)
Here's a link on 40D vs. 7D high ISO comparison I did before selling off my 40D. As many of the following comments had acknowledged, the amount of detail retained by the 7D (even when down-rezing to match that of 40D file) is quite noticeable.