BFG will never disclose this information, but short of P modes in other universes without a D mode option, the beginning will see the largest influx of cash for them, otherwise they'd have little to no incentive to rehash universes.
BFG doesn't have to confirm...whether you or I are right, the end result is still the same. I think more money is spent, by a player, as the game progresses. In the beginning more players spend money... As the number of players decrease, or just the players willing to spend money decreases, the amount per player will increase. For whatever the purpose, you seem to need (or want) more things the longer you play.
I swore I wouldn't spend money on the game...but even I have fell victim to wanting a commander, of some sort, from time to time or a p marker, or that awful money sucking synergist. LOL In the beginning, it's just not necessary, I don't think, but that's just from my point of view and a few of the players I've spoken to. I went through a period of unemployment and it was the best time for my game play...it forced me to do things without the aid of the store bought "helpers". I can actually play without needing to buy credits now.