I don't know about Light but you can't really cite Bruschi as an example. If, instead of signing his extension last year, he had gone on the open market, he probably wouldn't have gotten much more than he did get from the Pats. Now, he had an excellent 2004, but there was no guarantee at the time he signed his deal that that was going to happen.
And now that his career may be over, he's looking awfully smart for taking the money last year instead of waiting to become a FA this offseason.