"Can university math people contribute significantly to precollege mathematics education beyond giving future teachers a few preservice math courses?"
There is currently a lot of energy and talent and enthusiasm directed toward an affirmative answer to this question. But, in the end, the answer might turn out to be "No".
So what about all these wonderful new materials and in-service programs developed and run by university educators and mathematicians? Will there be any footprints left in the sand after the university folks go home, or get tired?
We are still doing things to teachers or for teachers, rather than doing things with teachers. We are also still thinking in terms of grants and projects rather than institutional change (both in schools and universities). If we continue to behave this way, there is the danger that there will, in the end, be no footprints left in the sand.