RE: Thoughts on price
It would be a good deal for someone specifically looking for a 9 and wanting an action job on it. Otherwise, you aren't going to be able to get much more for it than a regular used XD. It sure does help the gun sell...but most people will not pay more money for it, unless they want it in the first place.
Sight unseen, $600 is on the high side of fair. I would submit that $525-550 might help it move. 600 does give you some wiggle room...and you can always come down. Heck, I think thats about right. However, if you can't find someone who wants the action job....you may end up letting it go for 450 or keeping it.