I have been wondering that as well. If the spent movement points counter isn't reset, but instead lowered by the movement points per turn, then spending two movement points will make the unit get stuck for a turn. Perhaps capping movement loss next turn to max one or something.
Example:
A treasure moves with one movement point. The terrain cost one and it moves like it does right now. If the terrain cost 2, then it moves one plot every second turn. If the terrain cost 3, then it moves one and waits 2 turns.
I don't know if I like it because I have a hard time predicting the gameplay impact. It could be dull to get your units stuck all the time. Also the pathfinder would have to be rewritten to take this into account.