The trouble is stopping just short of the level at which (by minimum wage earner standards) they begin to live in opulence. That meaning, in this case, not so much when they're able to afford a yatch, but when they begin to consider putting on more debt than they can actually afford -- debt that won't get repaid. In that case, a vicious circle creeps in, because the ups and downs in excess debt levels contribute to inordinately sized booms and busts, e.g. like we have now.
So the real conclusion should be, since most people in developed countries earn barely more than the minimum wage itself: having a large consumer class benefits everyone in the economy provided that it is solvent.