Spending marks doesn't reduce the aquired weekly total, so swapping one for the other wouldn't impact the weekly cap. If they decided people would gain to much glimmer, they could have reduced or cut out the glimmer gain entirely. Now, people will have nothing to do with all their excess materials. Other than upgrades, there is nothing to spend them on and even more ways to aquire them. The exchange worked because materials weren't hard to aquire in the 1st place.