Don't get me wrong; I'm not saying that FA isn't key to building a championship team. Of course it is. But if 42% of the team is FAs, trades, and street pick-ups, then the other 58% is guys you drafted, and you have to hit on those guys.
What do Reggie Bush, Pierre Thomas, Marques Colston, Devery Henderson, Jermon Bushrod, Jahri Evans, Carl Nicks, Malcolm Jenkins, Tracy Porter, Sedrick Ellis, Will Smith, and Garrett Hartley have in common? They were all drafted (or UDFAed in Pierre's case) by the Saints, and Smith, at 28, is the only one that's older than 27. I'll agree that they skew more towards FA than most teams, but the fact stands that they wouldn't even be in that position in the first place if they weren't hitting on their draft picks.
Therefore, if the Pats want to sustain success into the future, then they have to hit on some draft picks, and hit hard. 2009 was a great start, IMO, and the four second-rounders that they have coming up give them a fantastic chance to build the foundation for another SB run. As upstater said before, rather than trying to hedge their bets, I'd rather they keep the picks and rely on them to hit on them. Because at the end of the day, if the Pats can't hit on picks, they won't remain competitive.
Everyone talks about how Greer and Sharper turned around the Saints' secondary, but I'd go out on a limb and say that Porter and Jenkins (23 and 22 y/o) had more than a little to do with it, as well.
And that's the point: even in the most extreme example, which you just gave, the Saints were only in the position to get over the hump with FA signings because they drafted *very* well over the past few years. So I stand by my original point, which is that NFL teams can't succeed without drafting well. This is likely to be less true this year, without a cap, but the cap will come back and in a capped environment you can't compete without rookies giving valuable production on cost-effective contracts.