Woohoo, way to turn an endurance question into a let's whine about donators thread.
putting a ton of time into the game is necessary -- high level donator or not.
not saying donating doesn't help (a lot) but you can't throw money at the game and expect it to make up for a low activity level.
look at Raf -- he's one of the top players in the game, highest in XP level by a healthy margin, and he has not donated much at all. He boosts endurance via career and buying credits on the market.
Thrillhouse hasn't donated a lot, either. He's not in the top 10, but he's also not nearly as old as Raf.
Donators keep this game going. Yay for us!