I am very cool with Mechanics being used for all of the other mods, but the Crystals themselves have always had a near mystical quality to me. As has been suggested by others, I think that a good alternative would be using the Discipline skill to modify the Crystals themselves. This could easily be modified further by adding boost dice equal to force rating. A lightsaber is a special, mythical even, weapon that has always seemed to require focus and Force Sensitivity to craft. Otherwise it would be a lightfoil, right? But the heart of the blade itself is the Crystal.
As another suggestion, the Lightsaber skill itself could be used in place of the mechanics check, especially for the more mundane attachments. I like the idea of using Ranged (light) to perform a mechanics check on your pistol. Perhaps at a higher difficulty though. This represents familiarity and focus on that particular item, rather than spending ranks learning how ships, droids, and computer hardware works.