Since level 20 rewards do not upgrade. I mean, till level 20 rewards increases when you promote, but from that moment on they get stuck in 14M for the first place. For someone who's in level 40 (or even less), has buildings level 20 or higher, is very few money, it's a low prize (you can earn that in a day). I think it will be more interesting if it keeps increasing, like what happens from level 1 to level 20.
That would be nice
don't use MB and you'll not need more money at level 40!