I admit to doing the same thing with the Super Mario live wallpaper, and with a Droid 1. It ruined my battery, but it was worth it. I remember being able to turn on some switch that'd get it to display the path it was taking through a level, which was really cool to me. I miss that live wallpaper — the Droid less so (even though it's sitting on my desk because it's the only thing I have running Android 2.x).

Besides that, my argument is that if a you spend a lot of time in your launcher, it might affect battery life in a somewhat noticeable way. Typical usage should have you in another app most of the time, but that's speculation on my part. I could imagine folks using their launchers a whole lot if they were packed with widgets that did more than just display things, but I've never had a lot of luck finding widgets I liked. Ultimately, if you or anyone else is concerned about squeezing every possible minute out of your battery, your best bet might be to have a solid black static wallpaper. Mostly comes down to priorities.

Edit: http://android.ccpcreations.com/mariolive ⇐ I think that might be the same live wallpaper from back then? Can't verify it right now, and I'm wary of installing foreign APKs these days, so exercise caution.