You bring up an interesting point with your observation that pigment dyed leathers essentially have an impermeable finish. If this is the case, then seat treatments that promise to restore natural oils, soften the leather, etc. are just so much hogwash, not so? The stuff's not going to penetrate the finish, anyway.
I mentioned this before, back in December...
http://www.986forum.com/forums/showthread.php?p=32395#post32395
The products WILL restore natural oils, etc., if they could actually get TO the leather. But the pigment dye is a protective sealer. It keeps the leather from getting stained from spills. It keeps the oils and conditioners out, too.
So, the redoubtable MNBox is right again! Save your money, boys, and use the dish detergent from the kitchen instead of buying leather conditioners at $20 a bottle.
I'd use Murphy's Oil Soap myself....