It's a serious problem, and I think the more children who "go to the nurse," the more others think it's a place they can go, too, so that each nonsense visit spawns others. I have had a parent whose child suddenly started coming frequently say, "I think one of her classmates was going to the nurse a lot and that's why this started."
I think it would help to have specific criteria of when to send students-I think to leave it open ended leaves teachers nervous not to send, even if they think a child is fine-but in my district, at least, management thinks that teachers shouldn't make any health related decisions even if it's something like a papercut. Which I think is so dumb, for lack of a better word! Sometimes the health office just feels like another place to go once a day, like the bathroom. Not sure how we can be expected to handle the emergencies at the same time as every little discomfort that is noted in the entire school.
(no, I don't have 40 years experience :-) and I myself am still in my 20s, but I never went to the nurse as a child-I didn't know there was one, and I certainly never would have even thought to try to leave school for something like a passing headache. And if my parents had been called at work for my bumping my head on my desk while picking something up they would have been extremely confused. Sometimes it feels like we are liability officers and not nurses!)