I would have to to agree what has been said here thus far regarding the 3808 vs. 2809....I was in the somewhat same boat as you although I was considering the 2808ci at the time which was going for $599 but I still chose to spend the $$$ for the 3808.
I do understand your reasoning in the rather small difference that 15 watts of power seems to make the price difference a little silly. However, there is more to it than that. The 3808 is a much more solid AVR. Where the 2809 weighs I believe 28lbs the 3808 is 40lbs...Not knowing the internal specs of electronics used, this must translate into a better power supply and amp section over all the lower series...
As had been mentioned...the GUI!!! This interface is just fantastic and I was SO happy I spent the money to have it. I had two Denon receivers previous to this unit and this makes set-up, tweaking, and all tasks a breeze to do---so much more intuitive than the previous DOS like windows...
Lastly is the internet expandability with the 3808ci. You do have the option to hook it up via ethernet to download updates as they become available or to stream music, which I know some members do here from their PCs to the 3808. Denon was offering the upgrade pack that expanded the Audyssey functions to Dynamic EQ and Volume for free to new buyers....don't know if that still stands....still have not downloaded it myself...
In any event, the 3808 is a clear step up in the Denon line that seperates it from the rest of the products....making the 3808 4308 and 5308 Denon's best three AVRs...
Hope this was of some help for you...