Desktop visualizer does exactly that for icons... if you select say, 1x2, you can then stretch an icon's size out to full screen, if you actually want using launcher pro, or the stock home launcher.
So long as the icons are at least 512x512, they will stretch larger in size.
I have one screen now with 4 large icons, and it works great for quick selections... I have music, camera, camera 360 pro, and an oversized cardock all on one selection screen.
We are always using gps, so extending battery life as much as possible is always an issue with us. We already have extra batteries each, but rather then swap all the time, dimming down and conserving seems to work out fine on most days.