In my opinion, Minecart Mania is for lazy people. Back in 1.8 when it was still down, like Raz said, we were still able to make millions. I was still a builder then, and I spent 2 weeks perfecting an auto farm powered by pistons, which made around 60-75K per harvest. If you put your mind at it, you can do a lot.
Her's a video of that farm: http://www.youtube.com/watch?v=mHvXQqOzjio&feature=plcp