Both guys likely come back at vet min, don't sap from the comp process, and have experience in the system.
But their value comes from their versatility.
Schilling has experience at all 5 OL spots. While underwhelmed at his opportunity at OC, he looked to be an adequate OG.
Dobbs was excellent before his injury. He was active as a run-defender, looked slippery, shredded blocks, and had natural instinct towards the ball-carrier. And while he wasn't as superb as a pass-rusher, I wouldn't judge him on his sack count, he was able to penetrate, disrupt, and get pressure in his pass-rush opportunities. He also can rush from inside or outside and had an ability to drop into zone coverage. Dobbs was the best of the band-aid free agents Seahawks signed during the season.
These signings aren't stellar by any means and they are replaceable talent. But their versatility and experience with the Seahawks last season is a certainly useful plus and they help the bottom-line on the practice field.