This is discussed by Abarbanel in his commentary to Rambam's Moreh Nevuchim (II:32).
In his interpretation of R' Yochanan, he denies that R' Yochanan is referring to prophecy at all when he says "God causes his divine presence to rest...". God resting his divine presence on someone is different from His granting someone prophecy. (What exactly "resting His shechina" means is a discussion in itself. Suffice it to say that Abarbanel believes that it has only occurred once with Moshe and will occur once more with Mashiach.)
Therefore, R' Yochanan's next dictum, "All prophets were wealthy..." in which he learns this from Moshe, Shmuel, and Amos, and Yonah is a very different issue than his first saying. This, Abarbanel explains, is not to say that wealth is a prerequisite for prophecy, but rather it is a simple observation that prophecy seems to help in acquiring wealth. That is, prophets, as a result of being the objects of "God's attention" in a way, seem to become blessed with prosperity and financial success. (Note that Moshe acquired the precious stones long after he experienced his first prophecy at the burning bush. Shmuel as well, when he experienced his first prophecy was merely a servant to Eli in Shiloh. They only became wealthy much later.)
Just to conclude, Abarbanel believes that there are no physical or material attributes that are conditional to becoming a prophet. (See also his commentary to Shemos 3 and Amos 1.)