But you don't always need more surface area, just something you don't want to wiggle loose, like say your cargo carrier on top of your car that's attached with hand wingnuts. I don't have enough experience with loctite to know if I want to spray it on that.
Yeah, a split ring washer there is probably not doing much. Possibly even making things worse.
Given it's more or less impossible to sufficiently torque a wing nut, there are actually not many great solutions...
A dab of low strength loctite would definitely help, but that's one-time-only and you've got to carry the loctite around if you want to re-do the connection... At which point why not just carry a spanner instead and just use a properly-torqued normal nut?
Probably the best would be to swap out the plain wingnuts for nylock wing nuts, which should at least help a bit.
I bought some split ring washers and they worked great. The nuts went from coming loose every few days on a long road trip, to not coming loose at all.
