Parting out a machine IMO should be the last resort. Not only does it make one more classic 'that' much closer to extinction, but I think it would be against the wishes of the original designer (sort of a weird karma thing with me).

For the parts that are already separate, go nuts.

For the machines that are in contention of being parted, that's a LOT of parts, and a LOT of work. Price them well, and they'll all move quick, and you'll have tons of good pinball karma for keeping them intact.