I have wondered about Spanx, I have heard good things about them. I carry most of my weight in my stomach area so it sounds like they might help smooth things in that area.
RE: the spanx tights. I haven't had much luck with tights in general unless they are really thick. I saw the Spanx tights and thought about buying them, but honestly it is cheaper to just buy the actual spanx and then tights to go over them....at least it is cheaper if they run all the time.
To me the knock-off Spanx they have at Target (forget what they call them...shapers or some such thing) are just as good and MUCH CHEAPER!
If we are thinking of the same thing, those are actually from the maker of SPANX and cost half the price. I think they are just as good also. The name is ASSETS® by Sara Blakely®. They have a few different styles in several colors and sizes. You can also get them from target.com.