I think that you'll notice a nice difference. I used a Dolby Digital-only Yamaha from 1997 for years, and two years ago I bought a Pioneer with the latest surround modes and (important to me) an auto set-up feature.
1. Surround modes: I enjoyed the addition of DTS, if only because I could finally experience it years after it was introduced!

On the movies that I have watched, the DTS soundtrack sounds better to me than the DD track.
2. The auto set-up for my Pioneer adjusted a five-band equalizer for each speaker, and that made a
huge improvement in how my system sounded to me. My speakers that had sounded bright and harsh with the Yammy became much smoother and more enjoyable. The 3808 has an auto set-up routine, as well, and I believe that it is more sophisticated than that in my $450 Pioneer.
So, yes, I say give it a try. I went from a $1000 Yammy from 1997 to a $450 Pioneer in 2005, and I was very pleased with the upgrade. Technological advances and dropping prices are a great thing. If you're willing to get a higher end Denon, I think that you'll be pleased, too.
All of that said, I'd highly recommend buying from someplace that will let you take it back if you don't notice a big enough difference to warrant the cost.