4S Ranch (92127) tends to have much higher Mello Roos. As for Carmel Valley you (BG) are still abnging the wrong drum. The newer subdivisions in the most impacted Elem school attendance boundaries within CV do not have exhorbitant MR. In fact they are on the lower end of the scale as most fall in $100 and below range.
By the way, dont take this as an endorsement of Carmel Valley as I for one dont particularly care for it. I much prefer the lifestyle in Encinitas/South carlsbad which is also in the San Dieguito schoold sitrict boundaries and has similar MR.