Good luck. This seems like it will take a while. I'm currently on a quest just to beat the game on the default settings (4 difficulty, 3 credits, 3 lives). I've been playing the game almost every day for months and still haven't done it yet. Tonight was the closest I've been so far. I made it to the giant rose boss (2nd to last) and did quite a bit of damage to it. I think if I had 1 more life I might have had a chance. I can usually get through the last phase without dying.
Anyway, in terms of unlocking stuff, the BG Graphics is the last thing I have left. I'm guessing the Elite Mode score challenge is probably the most efficient way to earn money, but I've mostly been focused on Arcade Mode. Still, I have about $24 trillion. I'm hoping I manage to beat the game before I unlock the BG Graphics though... --- Classic NES tunes in 5.1 surround! http://nes51.wordpress.com/