There is some small public finance advantage for public schools to take in out of state students for financial support, but this is a small effect.  I doubt you could detect the bond rating advantage, not that investors rely on bond ratings much lately.  The largest benefit would be in providing local businessess with more highly qualified workers.  That productivity increase would directlly yield higher incomes and higher tax revenues compared to holding those students back in inferior schools.

Andrew and Pete have both provided some very provocative thoughts about my earlier post about a county in Maryland selling excess capacity in its public schools to anyone interested in attending, and doing so by charging a lower tuition. Their comments on how resources are and should be allocated deserve much more discussion.