When we signed Colombo he sat for 1/3 to 1/4 of the end of the season. He then went through our off-season program and came in and competed in TC and won the job. Colombo wasn't signed out of desperation, he was a "rock overturned" project that just happened to work out. The Cowboys weren't counting on him for anything.
There's no less of a need to take a chance on Bentley (if the contract numbers jive) then there was to take a chance on Tank Johnson. We didn't need Johnson, it was an opportunity to pick up an amazing talent under a unique situation. That low risk gamble could pay some MAJOR dividends this season. If Bentley could be "observed" under similar conditions, you would have to be a fool to not at least explore the possibilities of signing a guy that was top 3 talent at his position a short two years ago. Keep in mind, also, that no one wanted any part of Colombo due to his knee injury history either. He's worked out quite well and will make a boatload of money in FA next year (either in Dallas or somewhere else).