We currently have a grass infield with the dirt basepaths. One school near us who has the full dirt infield nearly never has a rainout. They've got a full infield tarp so they can cover the dirt and leave it there. With a grass infield, you wouldn't be able to just leave it there.
Our school is going to building new fields in the next couple years. The JV field will likely be full dirt, but the varsity field is still up in the air. They've talked about not setting up water with the new fields so our coach has said he plans to go with a full dirt infield until he's given water.
Our current field is doing away with the dirt basepaths. Our coach has decided that they are too much work!