This is tough on many levels. We have the same situation for middle school. We are not at the middle school yet. I hear similar things about the teachers being better. For me it is more about DD being with her peers. I think it is tough for teachers to teach many different levels in a classroom. The magnet essentially groups the kids making it easier for the teachers to shine. There are many good teachers at all the schools they just have a lot to deal with IMHO with so many varying ability grouping. These same teachers at the magnet school may not relate to the regular classes.
We have enough kids that will go to the magnet that we meet lots of people that are in the same program. Sometimes I need to remember that it's not everyone so maybe I shouldn't talk about education issues.
My last thought was that as I initially researched GT kids I came to realize that NCLB makes it really difficult for the "bright" unidentified kids to get a challenge since teachers are forced by districts to teach the test and get scores. I wish more could be done for those kids - but I know the "GT" limits are set by funding issues. I wonder if it is these parents who "see the light" but get no help. They may externalize it by offhand comments not necessarily jealousy but frustration. At least even in the normal middle schools, I think most places have advanced tracks open to not only GT but high achievers or GT kids that don't test as well.