One in 100,000 is the number their research gives them, but that's based on reported symptoms by people who have been in a position to actually report them and be heard. Given the number of us here who have been patted on the head medically and sent on our way, I wonder how many more of us would have reported just such symptoms were anyone interested in actually collecting the information instead of sending us away to "learn to live with it"?
I think the only real way to diagnose spasm is to see it. Failing that, a less invasive method of testing that could detect hyperactive muscle activity through some kind of vibration or electrical discharge would seem possible. Even if you couldn't say for certain which muscles in there were the ones spasming, the very presence of spasm identified non-invasively would be a great diagnostic starting point. I've seen literature that suggests that the TT and the Stapedius present their symptoms somewhat differently when in spasm.
U are totally right, I have to agreed with your conclusion about number.
BTW. It look little invasive to do some botox injections without precise indications and diagnose that muscle spasm is present. And i have feeling that most of ENTs do not know to recognize it, that's why I ask @Mojo did those two clinics (where he got a positive answer) said something about diagnose.