I've used PS quite extensively for mass FRM editing. I've never created plugins, but you can do some nifty automations and batch conversions with it. For example: colour replacement, resizing etc. But yes, the decompiling, editing, and recompiling process alone takes hours. A plugin would be nice. But first i think you need enough manpower to do the art editing.
It is very unfortunate they never used layered sprites in FO, as it would have lent so much more modding potential to the graphics of the game.