I would like to see that being in Vacation Mode that it costs the player resource's for everyday in vacation mode.
So for every, hour in vacation it costs the player (0.05*Players total points in Spice) For every Hour in vacation mode. The player would have to select which planet to pay this on leaving vacation mode. If the player can't pay in spice it's same spice value is then applied to next most valuable resource.
To me Spice then Metal then Kryptonite and last would be Pig Iron.