Yeah blasting causes holes in thin spots, but then again so would a probe if you had checked there for rust

There are different types of blast medium, from sand to soda to ground nut shells, the softer ones won't harm the metal as near as bad as sand. The biggest thing you want to worry about in blasting is metal deformation on the really large unsuported areas (like the rear quarter panels

) any holes it finds are holes that should be repaired irregaurdless if you manually strip it or it's blasted.
Oh yeah, another big negative with blasting! dist and debris filtering out of the nooks and crannies spoiling paint jobs and making a general nuisance for a long time after the blasting unless the car is meticulously cleaned right after blasting!

You should try wire wheeling and how black you are afterwards...I had crap comming out of my nose for three days each time