An intriguing suggestion. The primary problem I have with it is whether that rendering of “elam” (or “olam”) can be sustained given the wider context.
This portion of Daniel is Aramaic rather than Hebrew. The only other place that I can see in which “elam” is applied to a kingdom is Dan 7:14,18,27. And this is most certainly referring to the messianic kingdom.
It is tempting to read Daniel 2-4 as a connected sequence of events as you have suggested, but I favor viewing the book overall as a double-chaism as proposed by William H Shea in 1986, although something similar was presented at least 60 years earlier by E.W. Bullinger for the Aramaic section (see “The Companion Bible”).
If this structure is valid then it makes sense that chapters 2 and 7 would both have messianic kingdom prophecies as their themes. Whereas chapters 4 and 5 would rightly be prophecies restricted to the kings of the time (Nebuchadnezzar and Belshazzar respectively). Chapters 3 and 6 then are focused on rightful worship, and the trials of God's people.
Add to that the phrase “all these kingdoms” in Dan 2:44. I am aware here that the words could be passed as “kingships” rather than “kingdoms”, but I cannot find a single Bible translation that has gone this route. (http://biblehub.com/daniel/2-44.htm)
As far as the material of the stone being lowlier than the gold, I don't think there is a problem. Evidently the gold, silver etc is from a human standpoint - not God's. Jesus was a lowly one - the stone that the builders rejected. It is only when his kingdom becomes a great mountain having fully crushed the image that everyone understands its superior value.
Similarly the fact that Medo-Persia, Greece etc, might have had more extensive dominions than Babylon is not necessarily important to the image as a whole. From Nebuchadnezzer's standpoint, his form of human government is pure gold. But the whole concept of human government is something that would be shown to have less and less value as the centuries advanced, until finally they are replaced by God's kingdom.
So whilst your idea is interesting and well presented, I still think that the messianic kingdom is the ultimate theme of chapter 2.