The cap problem is a phantom issue (as documented
here, among other places). We massage our salary cap as well as any team in the league.
As for high profile free agency turds... we may lead the league in those. We didn't pick up any last year, but we held onto Lloyd (partly because we couldn't shed Lloyd and Archuleta in the same year) and that turned out pretty rotten. The thing is, aside from the Patriots this year and the Colts (as you've pointed out), just about everyone has a free agent they'd rather not have grabbed. Someone is always taking up too much space on someone's roster.
Even New England has players that are probably earning more than they are producing. I could easily argue that Donte' Stallworth is overpaid on that roster, considering the production his teammates have put out. He makes $225k less than Moss on the cap, and over a million more than Welker (thanks,
PatsCap.com!). They have a backup FB (Kyle Eckel) counting for $5.6 million on this year's cap!
My point (and I do have one) is that nobody does this perfectly. There are a number of teams that believe if you hit on half your picks after the first round, you are successful. It isn't realistic to expect the guys from rounds 4-7 to be quality starters, it's just pleasantly surprising if that happens.