I had the hull sandblasted on my first boat, a 26 foot sloop. It had hundreds of blisters. I queried many, many of whom recommended against it. The yard owner recommended a guy who used the ''right'' sandblasting medium that wouldn''t remove all the gel coat. His work opened up all the blisters. I washed the hull in fresh water, almost daily for two months before it fully dried out (some spots were wet, checked with a moisture meter). I faired very few of the deeper blisters, applied West Epoxy over the entire bottom, two coats of Interprotect 2001, then bottom paint, and crossed my fingers.
Three years later I hauled the boat for new bottom paint. Not one blister! Boy was I happy!
Overall, the job was still messy and miserable, working at backwrenching angles in the hot summer months.... but I''m getting ready to do it again, two boats later.... not as bad this time though, just a few gel coat blisters, dime sized and smaller...