There should be new knowledge and building upgrades. t level 40 with everything maxed i have nothing left to grind for and therefore much less to spend on i believe that building levels should go to 45 or max at 50, i know that you need to turn a profit as well. So maybe from level 41-45 it should cost diamonds and from level 46-50 it should cost diamonds and precious dust. I just feel like the game is slowing down as i and many others have much less to grind for aside from town skins.