The Riches of Moshe

The Gemara in Nedarim 38 (recent daf yomi) made the following statement:

אָמַר רַבִּי יוֹחָנָן: אֵין הַקָּדוֹשׁ בָּרוּךְ הוּא מַשְׁרֶה שְׁכִינָתוֹ אֶלָּא עַל גִּבּוֹר וְעָשִׁיר וְחָכָם וְעָנָיו, וְכוּלָּן מִמֹּשֶׁה. 

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עָשִׁיר — ״פְּסׇל לָךְ״, פְּסוֹלְתָּן שֶׁלְּךָ יְהֵא.

The Gemara states that to be a Navi you have to be rich, and learns it out from Moshe. Moshe got rich from the luchos, when he made the luchos out of precious stone, he kept the extra which made him rich.

When we think about this it's quite difficult. 

1. There is no objective criteria to being rich, it is in relation to the people you live with. If everyone in a society lives the same can we call a specific member of that society rich?

2. Precious stones only have value because people assign them value. 

Both of these are relevant to the Midbar. 

1. What would it mean to be rich in the midbar? Food and water was provided free of charge by God. There was no land to buy, and everyone had a tent. So what exactly did it mean that Moshe was rich? How did his wealth express itself? They were in the midbar so there was nothing to buy either. So how was Moshe richer then anyone else?

2. What were precious stones worth in the midbar? They are only valuable because they are rare and have some use. Why would they have any value in the midbar? What use would they have?