The "extra FoV bit" is pretty substantial and well worth getting in itself; as of DKS, the rest of the game has been somewhat rebalanced, too, so it plays a bit more smoothly in terms of overall difficulty and convenience. I seem to recall the graphics have also been somewhat improved in DKS, but I'm much too unobservant to say what they've changed! As far as I know, the developers' console is the main addition to the Director's Cut, but you have to admit that playing through the whole game as a chicken has a certain attraction all of its own!
Regarding the savegames, even if you still had them you wouldn't be able to load them, they made too many minor changes for them to be loadable; but you can launch straight into FoV without having to go through ED first.
