A positive environment was always something that I had in my classroom. "music for music's sake" was my philosophy. When the students passed off a scale they got an A whether it took them 10 tries or 1 because I didn't care about the grade. I cared about the skill. Kids having the coordinate sheets is about the skill. And I didn't need to really fuss at kids because their peers did it for me. At the end of the day, what we accomplished in rehearsal was up to them. So the kids that wanted to be good pushed the kids that weren't sure. THAT was the positive environment in a healthy program. The kids didn't need stuff or ice cream or anything else. They needed success, (measured by each student, not always a global contest rating).
Sometimes you have to deal with negativity because sometimes things are bad. Bad sounds, bad shapes, bad timing, bad fingers.
I don't need gimmicks or a reboot of the entire system. Teach kids to have better work ethics and teach them to be better musicians. Pretty simple.