What if luxury resources could be spent on an outpost to accelerate colonization? Sometimes luxury resorts are stacked, you have 999 blue mushrroms and can only be sold in the market... yes, you can use them to build some improvements and to accelerate population growth a bit. But in the late game, the cost of these boost is irrelevant.

EDIT: With the new update, the luxury resources manage are really ok. You can forget this IDEA if you want.