I don't know breeding genetics well enough, but it seems to me that the best stuff will usually be the stuff that's all recessive genes. When you try to cross it, you'll lose whatever makes it great. I think that's how it works in other industries - any F1 seeds are always crap.. When you think about it, there are clone-only strains that no one has managed to reproduce - Blue Dream, Kali Mist, etc. - just perfect combinations of recessive genes. Of course, it's gotta be hard to produce those stable seeds in the first place.
I just remember hearing about flower and garden varieties that produce seeds but whose next generation are either sterile or crap.