Not sure what u mean by potential up, potential doesn't change.
and have no impact on dmi, the maximum for dmi is around "salary today" * 10, it can go a little higher but not much.
So it is only skills and gameshape, and when some beginners get the help that they should make their lineup by salary i think the dmi would help then more, when you also mention that gs plays a big role so you shouldn't watch out for it while buying players.