Yeah, I hear ya....its kind of a sticky wicket. On one hand, you don't want the big 6 to become nothing, on the other it sucks to be at a WCC/MVC/CUSA school, consisitently winning NT games and be at parity with a PT level Duke program.
No super easy answer. I think the general consensus is some combo of less baseline prestige and looking more seasons back. Maybe with some addition of a baseline worst prestige as well.
One of my old proposals was to keep baseline prestige, cut its value in half, and replace that 50% of baseline with seasons 5,6,7 and 8 ago.