I think that if you like them and they are special to you, then yes, make a diaza for them. I would be interesting to see what you come up with, I have always wanted to try my hand at it, but I am not that good at wood working. I find the first stone the most interesting.
Most of the waterfall stones that I have seen look more like a far off mountain ridge with the "waterfall" coming between two of the peaks.
John