Burgess,
I think the self cleaning feature is nice, but I certainly don't think it's a necessary option (at least for me).
I mainly shoot a MkIIN, a 20D, and a 40D.
I was having some dust issues on the IIN because I use it more than all my other bodies combined. A few years ago, I picked up an Arctic Butterfly. I went over all my sensors thoroughly, and since then have only used the Butterfly if I noticed a problem.
The key is just to be careful when changing lenses. I usually carry 2 bodies when shooting. One of the main reasons for this is so I don't have to swap lenses as much.
Keeping sensors clean is to me more a case of practicing good prevention rather than having a good method of cleanup.
Telephoto lenses don't inherently stir more air. The only lenses you have to worry about this with are push-pull zooms such as the 100-400 or 28-300. You will see these referred to as "dust suckers". I'm not saying their not nice lenses, but they can cause more maintenance issues.
To a lesser degree, you will face the same situation with any lenses that change length when you zoom or focus, such as the 24-105, as they are still displacing air.
Having said all this, I'll leave you with my 2c...
1) While a self-cleaning sensor is nice (and I do believe they help), it is not one of key features I need, and lack thereof would not be a deal-breaker. I personally wouldn't purchase a newer camera for this alone.
2) If you decide to upgrade in the future (and face it, most of us here understand the overwhelming desire to do this), hang on to your 20D (sorry csshih). There is just something about the sensor in the 20D and the MkII series that sets it apart.
I have used everything up to the MkIII's and the only one (IMHO) that exceeds it is the original 5D. No matter what in-camera settings I use, the images from this sensor have that "feel". Kind of like the results I used to get from Fuji Velvia.
Hope this helps...
Rich