Probably overkill, but I can't see why it wouldn't work well. It's not going to be as stiff as 18AWG, so you should be fine provided you have decent routes in the guitar to get from cavity to cavity.
I just replaced everything in my Epi Les Paul last night and i used 20 gauge wire for everything thinking it would be easier. WRONG! It worked just fine, so don't sweat using it. It's just tougher to bend. i would limit it to areas where it can be used in longer lengths. In other words, don't go from one pot to another, but going from the jack or the switch to the pots is fine. The shorter lengths are just tough to work with. But at the end of the day it worked fine with no functional problems.