Is it not greater to fulfill Mitzvos without being commanded?

Anaf Yosef, Rav Y. Emden: There is a greater display of love of Hash-m when a person fulfills without being commanded. However, in terms of reward, one who is commanded has a greater Yetzer Hara challenging him, trying to prevent him from fulfilling it. Thus, his reward is greater when he does fulfill it.

Tosfos, Daas Torah: One who is not commanded might not fulfill it when things get difficult, but one who is commanded, meaning that he is acting out of fear, will fulfill it even when it is difficult for him.

Sefer Ha'ikrim, Maharal: In addition to actually performing this good deed, he is also fulfilling the will of his Creator who wishes him to do it.

Does the Gemara not say in Yerushalmi Berachos (7a) that anyone who is exempt from something and he anyway does it, he is called a commoner? (Ramban Kidushin 31a)

Ramban (ibid): That Gemara refers to something that nobody is commanded to fulfill. However, if people are commanded and one particular individual is not and he fulfills it anyway, it is considered a Mitzvah.

Meiri: That only applies to things that do not give any type of understanding, moral lesson or personal growth.

Ein Eliyahu: That Gemara refers to a situation where, by being stringent in that Mitzvah, it leads to a leniency or lack of observance of another Mitzvah.