Everyone has problems finding good players in FA. That's why staying out is a good move. Given the success rate in FA is pretty bad, and given that even when you do finding a contributor you likely overpaid for them, standing pat and overspending less for marginal players is a good move.
The best teams in free agency are teams like the Packers and Ravens who never spend a dime, just collect compensatory picks, or teams like New England and San Francisco who pick off under appreciated older players late, late in the process on cheap short term deals.
Arguably we should be doing less. Certainly not more.
But, since you asked, Saints FA successes
Ben Grubbs
Curtis Lofton
Jabari Greer
Darren Sharper
Darren Sproles
Drew Brees
We've had some success. Franklin wasn't that bad for us either, our decision to not retain him had more to do with Spags replacing Williams than his performance I think (less 3-man fronts).