Hmm...well, the moon's greater gravitational pull can also affect animals and people (I read somewhere that due to the full moon increasing our blood flow or pressure or somesuch, our primal natures surface more, leading to increased crime rates during the full moon). Maybe that could be the justification for affecting such things as Foliage...
Or maybe we should just scrap this idea and make a new card based off the "Field spells and permanents affect one extra space" thing?