Ultimately here is what I did with the Thief template in my GURPS DF game.
Use Thief as written, except:
- Remove Filch (saves 2 points)
- Remove Smuggling (saves 2 points)
- Remove Shadowing (saves 2 points)
- Move Perfect Balance from a required Advantage to an Optional Advantage
- Reduce Urban Survival from Per+1  to Per 
Put the 22 points from this into:
- 20 more points of Advantages (total 50)
- raise the Melee Weapon skill from DX-1  to DX .
- raise the ranged weapon skill from DX-1  to DX .
Also, although I normally restrict new PCs to just the abilities on the template itself, for the Thief I do allow unrestricted purchase of any Power-Ups. While I like the idea of a restricted startup set and Power-Ups as those first new things you get to learn, many of the Thief Power-Ups are too important to a Thief's success right out of the gate.
And don't forget, in DF, picking locks and removing traps are both DX-based tasks, not the more realistic IQ-based task it is in Basic Set.