I see the case for pessimism, but I look at teams like the Steelers who don't break the bank (except for keeping a couple of stars) but still remain consistently good. Trends come and go in the NFL, and I think it's the teams who can stay ahead of the curve who will have a competitive advantage. Unfortunately I'm a bit nervous about switching to the 3-4 as it seems like more of a case of following the trend rather than setting it. The Steelers had success because they could pick up players cheap who wouldn't fit in other teams' systems, but I'm thinking the bargains are no longer in good 3-4 players.
In any event, though, once you get past the real stars of the game, I think that players become, not interchangeable, but very dependent on the system you run. If the Redskins and Cowboys drive up the price for current stars, it will be critical to find no-name players who can play a solid role on your team. That's how the Steelers did it, that's how the Patriots did it back when they won their first championship.