Keep it the way it is. The only "tanking" is minor and only among a few teams that are already at the bottom - if at all. The "Suck for Luck" season of the Colts was an anomaly. If we start seeing more of that, then maybe we look at it. We haven't had the rookie contract system that long and prior to that the bottom 5 teams were saddled with high value contracts that crippled their cap situation. Nobody wanted to trade in to the top 5 picks because the value wasn't there.
Since 2000, 13 NFC teams and 10 AFC teams have played in a Conference Championship game. The parity system is working pretty well.