Vigilance was kind of lame though, impacting the difficulty of critically failing a stealth roll. But the more I thought on it this seemed like a waste of a power (and something I will be, much like with combat, in fact EXACTLY like with combat, basing upon gear). So I took a cue from two successful powers from other classes: Weapon Specialization and Silver Tongue. These allowed the re-roll of damage dice (or influence dice as the case may be), selecting the better result.
So 'Expert' was set to use the same mechanic, however I didn't like the idea of all stealth rolls being equal; I wanted a character to be able to be better at hiding than pick pocketing, or wearing a disguise. The player with the power (much like weapon specialization) could select 1 type of stealth action (including keeping watch, or tracking, etc) per pie piece they have selected in rogue. This allowed them to force the re-roll of a die and choose the better result (lower if they are hiding, higher if they are keeping watch). In the case of conflicting roles (Expert Hider VS Expert Seeker) simply roll one die as normal.
Initial tests went well, though we shall see in extended play.