[Cibbwin]

I think that, more than anything, Gimli handing Gandalf the crown was to give closure to the fellowship, and indeed all the main characters. Aragorn is being crowned, Gandalf is crowning, the four hobbits are being honoured, Legolas is leading the elven entourage, Eowyn and Faramir are together, we see Eomer, we see Arwen finally reunited with Aragorn, and later we see Elrond, Galadriel and Bilbo, and so they have Gimli hand Gandalf the crown. Simple solution, and in a way, it works subconsiously, because Dwarves have a love of all things crafted out of metal.