The other thing contributing to the problem is all 40 cars are basically the same. You have 3 teams supplying the entire field. Gibbs, Hendrick, and Penske. All the lesser teams are either buying good used stuff, or leasing new from the big 3. This puts everyone at the same speed. Just look at the qualifying speeds from 1st to 40th today compared to the qualifying speeds from say the 1972 Daytona 500. Probably 10 mph difference from 1st to 40th back then.
Back in the day all teams pretty much built there own stuff with whatever budget they had. I think thats where the seperation of the cars on the track came from. Think about it. If back in 1972 everyone was suppled cars from Petty and the Wood Brothers, the competition wouldn't have been closer.