Let"r Rip! As long as your blast media isn"t too aggressive, you"ll be fine. I use glass beads that are like 80 grit paper. It leaves a very slight roughness to the diecast, but your first coat of primer will hide it completely.
I blast them, shot them with a self-etching primer, lightly (600 grit) sand the flat (sheet metal) areas, shoot a good coat of filler primer, body putty any imperfections you want to hide, shoot those spots with another coat of filler primer, repeat with putty if neccesary, wet sand the easy areas with 600, and shoot paint.
I have wet sanded the paint and re-shot to get a really pretty finish.