Jason,
I actually like the idea of rating a set of mixed tees. If you play one course quite often, it can add some variety, and I like the idea of having a number of different 18 hole yardages for people to choose. We have a "members" set of tees at Kingsley, and I think it's a pretty good mix, though I agree that it tends fall along "long hole - blue; short hole - gold". I'm actually surprised more courses don't do it, since I would assume the costs associated with doing so would be minimal. I'm not sure what is required for the USGA to come out and rate a set of tees.
One course that (as of my last visit) did not have a mixed set of tees, but which I thought desperately needed it was the Trophy Club northwest of Indianapolis. It's a great golf course, but it plays 7,317 - 75.3/138 from the tips, 6,580 - 72.1/130 from the blues, and 6,006 - 69.4/124 from the whites. I felt it was a little too short from the blue tees, but too long from the tips. Something right around 6,900 yards +/- would have been perfect, and they can put that together without building a new set of tees.