Agreed: no one I know would want to sign up for such a thing either. If all the expense and privacy invasion is just for the privelege of never being "selected for additional screening" , then the point is moot because most people don't get selected all that often. I'm sure most people will fail to see the benefit unless they get some other preferential treatment than just being exempted from the SSSS line.
I hope the gov't makes it really expensive, too. I can't imagine that they could do much of a background check on someone for less than a thousand dollars. A real security clearance (SCI compartmented or Q) can cost ~$100,000