The question is the following: do mitzvot have intrinsic value, or only extrinsic value. A ramification of this is the following scenario: A person has two ways of performing an act; one of them would fulfill an optional mitzvah (see below), while the other, for technical reasons, would not. Assuming (in this thought experiment) that the positive effects of mitzvos (e.g. improving one's character traits and improving society) would be identically achieved with both acts, is there any advantage performing the act that fulfills a mitzvah.

The question comes down to whether there is intrinsic value to the mitzvot.

A corollary of this question is whether one receives divine reward for the mitzvos themselves, or only for the resultant benefits (e.g. self perfection). 

What are the views of the Rishonim (medieval Jews) on the matter.

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Note: I am not asking whether there is extrinsic value to the mitzvot; i.e. ta'amei hamitzvot. I am asking if there is **only** extrinsic value in the mitzvot.
I am also not looking for the views of the Zohar. Furthermore, I am aware that one who violates a negative commandment, or neglects a positive commandment faces punishment. This would certainly be a reason to perform them. However, this is not "intrinsic value". Thus, the practical relevance of the question is to mitzvot kiyumiot (optional mitzvot).