If teachers' unions ever agree to let teachers be paid based on how good they are - rather than just by seniority - you might actually see more attractive salaries for good teachers. You might also see more bright people interested in taking up the profession if they knew they could make a better living doing so.
The problem is in the measuring of "good" - this is realistically best measured in terms of outcomes - i.e., the better a student does a the end of their scholastic engagement, the teachers involved should be rewarded. Problem: this takes long-term thinking and doesn't profit private interests.
Some teachers had a profound impact on my education. I spend the majority of my educational years in US schools, after immigrating here. The impact could not likely have been measured within the year. You would have to have looked at my performance at the end of several years, or my matriculation out of the school to accurately see what those experiences did for me.
However then you run into the problem that a similar students in similar classes with perhaps abusive home environments, or being unlucky enough to live in more dangerous neighborhoods (gangs, drugs) who might have completely different scores - so you'd need to also cross-correlate with socio-economic factors to get a true view (i.e., factoring out economic standing, and possibly more uncomfortable factors like ethnicity and type of household like single-income vs. dual, vs. single-parent, etc).
All this shit is hard. And doesn't profit those who want to cash in on the education cash cow. So it's never going to happen. But it should.
