yes, but not linear by a longshot.
Currently 1 point of spirit yields 5 times more mana return than 1 point of int.
As gearlevel rises, the disparity goes up.
spirit regen rises with the square root of int, linearly with spirit. So at higher gear levels, another point of int will give you less mp5. And at higher gear levels, another point of spirit will give you more mp5 than it does now.