Even if the group doesn't sit around for a whole day to heal, the one with fast healing still recovers their HD in HP at the end of the day. If the group does sit around to recover, the guy gets even more. So, it's nice in a game that has a fast pace or doesn't allow for rest stops often.
Heck, even with frequent rest stops, I'd take it. At mid to high level, this is a nice bump in free healing every day. Kinda like having the monk's wholeness of body ability.
My first reaction to the druid wildshape point you brought up is to say it would work that way. Basically it will add a few extra HP when you change back. But, I'd have to think about it more before I am sure. I don't have my books right now, but I don't see anything wrong with it. Isn't it HDx1.5 instead of HD? Or is it x2?