I do as swiftnick does, although this sometimes only works for getting flock/sand off rather than releasing the figure itself.
To get the superglue bond to break, you might need to put the figures in the freezer to make the superglue joint brittle, and then try gently prying them off with a strong blade. If you soak all the PVA and flock off, you may be able to get away with using a little bit of superglue debonder under the model to help break the glue too, but you risk damaging the paintjob like this, and the debonder is not especially cheap.
I'll be honest though; if the models are only painted quickly, and everything is metal, it can just be easier to dump the lot in paint stripper (acetone or something like Biostrip 20) and then rinse off the models, rebase, re-prime and re-paint. It may seem like more work, but if you're struggling to get the models off their old bases, and you can't cut the old bases off or incorporate them in the new bases, and if they only had a basic paintjob anyway, you'll spend more effort and time (and risk damaging the models) than just starting again with them.