Don't know that I would call this "extremely rare."  Like most Hot Wheels sets, there are relatively few compared to the gazillions of blistered cars.

I seem to remember this set from the '70's, and if the cars are original to the set I would guess late '70's or early '80's.  No big deal...just one more attempt in a continuing effort to build a better mousetrap...or in this case a better two lane launcher race track.  They've done several over the years, each a little different from the one before...but not what I would consider "rare."