Oh, man, do I work. The only time I have received a full class ovation was in Calculus. http://jd2718.org/2011/10/17/every-teacher-should-have-one-of-these-in-their-career/
But there's just no way to compare teaching kids who are prepared for advanced high school mathematics with giving younger kids their first taste of proof in geometry, or teaching algebra to kids who still trip on fractions, or confuse x^2 with 2x. The level of challenge for the teacher is much higher with the younger kids.
There are schools where math teachers' programs generally include one older prep and one younger prep. This is even more striking in 6-12 schools (Fieldston, at least when I visited 10 years ago, did this). I've also seen it this year (I'm on sabbatical, and have visited a dozen schools, of various types, in and out of the City). I think this is an excellent idea.
Teach down for one year, and see if you don't agree.