[Dave Rifkin]

Have you considered loaning them to a collector car museum? This way you still own them, they aren't in your face causing stress and if the feeling truly is gone you can sell them at that time.
At least this way; if you get the itch back by having them out of your hair for a while you can always go pick them back up and enjoy them again.
There are too many people with "the one that got away" stories; only in your case it would be "the ones that got away".
I would think long and hard about letting these cars go.