Still 100x better than what we have at S. I remember Ed Reed was way past his prime but still pretty effective in Houston. Thomas would still have some tread left. Well worth a reasonable contract.
I agree that some players can play well late in their careers, but Ed Reed does not help your case. He was cut by the Texans 7 games into a 3 year contract after registering only 14 tackles and 0 passes defended there. That said, he did get 3 interceptions for the Jets during the last 7 games of his career.
Now Rod and Charles Woodson. Those two played quite a few good/great years each late in their careers at safety. Rod had 39 of his 71 career interceptions after a season ending injury at age 30. Charles had 38 of his 65 interceptions after missing 21 games during the 3 injury plagues seasons right before he turned 30. The two combined for 10 pro-bowls appearances and 4 all-pro selections after turning 30 and dealing with injuries.
It's not out of the realm of possibility. For the right contract it could be worth a shot to see if he can repeat that.