1.5 came around, and you still cannot buy the class buffs with cartel coins even! ***!?
I think they are trying to leave some reason to consume content in place. Never been easier to level for what its worth. Level 40 or so and you are good to go.
That said, they probably could make use for having high legacy level, such as accessing your other toons companions and crew skils at 50; then let your purchase the buffs.