I think the trouble with numbers lies more in memory than anything, though perhaps for the same reason -- their innate abstraction -- that you described in the OP, Cusp.

It isn't that the numbers are changing on us because of their material vagueness, I think, so much as it is that we have difficulty in dreams attaching usable metaphors to numbers of any kind of complexity. Come to think of it, we have the same problem in waking life, but at least in waking life we can "retain" our number generations by grabbing a piece of paper and a pencil. In dreams, writing them down tends to fail because memory doesn't supply enough information to our unconscious to hold the written stuff steady (though, oddly, if you forget about the meaning of the symbols on the paper, they will seem to remain unchanged for quite a while).

So I think that to retain numbers in dreams you need to produce a metaphor that your memory can both readily file and find files that relate to it. That Stonehenge-like image you use for lottery numbers is an excellent example of this, BTW.