[...] the other demons would just [...]
That assumes universality.
There just need be enough strong demons that can be swayed by money/luxury, to put the most foolhardy demons in line. Power is like electricity in that it's the ultimate currency, but it's the people (or in this case Demons) that are the converters.
How much is enough depends on specifics, that is not to say that there would be a very powerful demon that could be swayed, nor that weren't there a powerful demon that would take an issue with it, but this world is much less set in stone and settled down politiclally than our own.
I'm not saying that demons are "live and let live" cause that's obviously not the case, but situations on the lower rings don't permeate to the higher ones and vice versa in most not politically active societies, and the conflict isn't about getting you and your allies to either ally with the current rulers or dominate each possible sphere, as it is to have your own place and protect it.
In that sense only the ones who would suitably benefit from "toppling over" (or were directly harmed by creation of) the money kingdom would actively pursue it's destruction. Other than that it would be some opportunists, some fools, and people who have their own deeply held reasons to oppose such a kingdom.(Think Baal motivations, or Clan/Family rivalries, although we have see nsurprisingly little of such in the story itself, probably due to a)Most clans that would end up opposite Delkira being completely destroyered during his rule, as we had read about Caim clan almost having such fate against an unspecified Demon king, and b) Great Valley war going on, whatever that is.)