I`d suggest that you pull each plug in turn when the engine is cold, rest the thread of the plug against cam cover bolt cap and then hit the starter and see what sort of spark your actually getting.
If they all check out ok then rig up a remote fuel feed so you don`t need to have the gas/fuel tank on and try starting it in the dark and see if you can see any sparking off the ht leads or coils as there shouldn`t be any.
Next step would be to replace the ignition trigger pickup as these can go out of resistance and then cause a weaker pulse than it should be putting out.
If you`ve owned the bike for as long as you say then i can`t see your bike all of a sudden changing it`s fueling setup all by itself.
Give these a try and if that doesn`t get it sorted out then will need to start on the next step of trouble shooting.
By the way, just because a the pickup coil might read ok on a resistance check then that doesn`t always mean it`ll be ok when under load.
Cheers, Matt