I like the simple mechanics. This would enable some pretty cool decks.
Difficult to say about the cost without testing it. 8 and 7 are probably pretty good seeing their cost also drops when you play these cards.
Once again my only real beef is the theme. It seems like by making cards less
heavy, they somehow become less expensive? I think that in order for the theme to work, it would have to be related to quanta somehow. The creatures you play when this card is active, are not cheaper because they are less heavy, they are cheaper because they cost less quanta. Of course once could also make the argument that they cost less quanta because they don't weight that much.