Like all customization, the answer is, most people won't use it.
I believe I have to agree with that statement. I know you go on to say and explain why you think animated wallpapers will be popular. It maybe unfair to just pick that one part, sorry.
Using myself as an example, when i started out here I changed my bootskin and login to the same skin of my WB, if there were ones, or tried to match the WB as best I could. I used screen savers and tried the match the theme in the same way. Those have pretty much been forgetten. Just aren't on the screen long enough to matter.
I generally keep a pretty clean or uncluttered desktop. I use OD+ but hide them when not in use, same with the regular Windows Task Bar. Same goes for Desktop Sidebar which I use. Yes there are some widgets and gadgets on the screen, usually those that go with the WB. What I'm getting at is with all the things that can be on the desktop will an animated wallpager be seen or just lost.
I have not doubts that people who can run them (Vista users) will try them out and run them for awhile. Even if they don't use much in resources I kind of feel that some of the folks, not all, will just go back to a nice static wallpaper that goes with the WB theme.
Now I'm not just saying this because I don't run Vista. If I had Vista I would try them. If fact I try everything that is available to customize the desktop that you provide to us. I do have to say though that after the first look at some they don't find there way back on to the desktop. I guess it has to do with duplication of efforts, several programs doing essentially the same actions. Okay off subject.
I think it's great that Stardock is able to provide animated wallpapers to more of the Vista users. You folks just keep coming up with more and more enhancements.