I started out that way, in fact my first skins were 3072 resolution. After a while I came to the conclusion it isn't really worth it, the file size becomes enormous and the graphics program slows right down. While you gain some accuracy, unaliased panel lines become aliased when the skin is shrunk, the whole thing can look a little fuzzy up close.
All I do now is enlarge certain items like complex noseart. These are created as seperate multilayer images two or more times oversized. When finished I make a copy of the file, merge the visible layers on the copy, shrink it, then paste it into the main skin.
