RE:WD 40 and Fly Lines
I prefer Boeshield T-9 over WD-40 for spraying equipment down. I try to never get it on my lines, but I have and it hasn't had any detrimental effects as far as I can tell. The T-9 acts as a lubricant and surfactant, but it also dries to a waxy consistency which doesn't wash away like WD-40 does. I've never tried spraying lures or flies, but would not recommend the T-9 for that.
I found a bottle of clear100% silicone liquid in an auto parts store and use that on a rag to clean/lubricate my lines when I remember to do it. It really works well and seems to last a while too.