I heard stay away from Grand Cayman - expensive and full of picpockets. My co-workers both just went to Cabo San Lucas and said it was beautiful. Only the food was expensive.
mm.. we were thinking of going to Cabo actually. We found some cheap all-inclusive packages. (Presidente in San Juan del Cabo I think). I guess if we got sick of the food they have there, and had to eat out at other restaurants, then the expensive food thing would be a problem.
Check the Western Regina in Cabo. If you really want my help, my co-worker can get discounts. Call me, you have mi nombre. :)