Have it the higher your psyche the less experience points it cost to use the hearth magics, like 1 psyche = -1 to experience use.
So for example at 10 Psyche (the starting number) would be the default 2000 xp for Commune With Nature, but at 11 Psyche it would cost 1999xp, at 12 psyche 1998 xp and so on.
Since on every character psyche seems to be like left asside kind of base attribute, so maybe give it more of a reward to pursue it.