I have NEVER said that I no longer need to learn anything about what I do. Nor have I said that teachers who are unqualified should be teaching in schools. I think it VERY important that in primary and secondary schools, teachers SHOULD be qualified. But just because they are qualified does not make them good.
You can think that I am rationalising all you like. Yes, I have 15 years of experience, but NEVER have I stated ANYWHERE that I am qualified more than I am. All of my students/parents can see my degrees and those of my other teachers, we post them up just for that reason. If presented with the opportunity to further my education and get a PGDE, I will take it.
I think that we should also distinguish where/what is being taught. Personally, I think experience is more important for what I do. Of course, the playgroup leader must be a native-English speaker who speaks correctly and with an intelligible accent, but for me, personality/experience is much more important. Now, I'm talking children 1-3 years of age. For children in primary school, I would have far different requirements for hiring a teacher.
If I open a kindergarten as I've been asked to do by many parents, I would ONLY hire fully qualified teachers. I have no problem with that whatsoever and would insist on it.