2007 was a once in a generation thing, I'm not expecting a repeat. Even the very low end of 400 points is respectable by NFL standards; that's 25 points per game. 28 ppg is considered to be very good and would be better than what all 32 teams did last year, yet that is less then 450 points. And 31 points is a big number to attain in a game, but is a huge number to average throughout the entire season - yet that is less than 500 points total.
I would say that 450-500 is an optimistic goal but would not be the least bit surprised with a total in the 400-450 range.