Safety wire is used for just in case. You say a properly tightened plug won't come off. OK. And you are never going to make a mistake. Safety wire prevents the consequences of the mistake.
No I don't lose sleep at night over whether I have remembered to tighten my drain plug because I tighten the damn thing
immediately as a part of installing it. It's not a multiple step process to install a drain plug. And, if somehow I were distracted (or drunk) enough to forget to install the drain plug the big puddle of clean oil on the floor would be a sure tip-off.
What about the caliper bolts. Do you safety wire those too? Or the axle nuts? What about those fork pinch bolts? There are numerous fasteners that you don't want to come loose, shouldn't they all be safety wired?
Further, most people on this forum recommend less than the Yamaha torque spec for engine drain plugs. If I am going to use half the factory torque spec, I am going to safety wire it just in case.
Seriously... hasn't this topic been beaten to death yet?
The incorrect torque spec is on the ENGINE oil drain plug. The manual says 31 ft-lbs, which is ludicrous. That is the one that gets stripped.
The (correct) torque spec in the manual for both the FINAL DRIVE fill and drain plugs is 17 ft-lbs. I have never heard of a final drive drain or fill plug being stripped, or coming loose if torqued to 17 ft-lbs.
As observed earlier, it's the same damn plug, threaded into soft aluminum alloy in all three instances.
17 ft lbs is the correct spec. It will crush the crush washer (if you have one) and will be tight enough to not come loose.