This is an SEO delight. You can search out highly ranked GeoCities sites that are also listed in DMOZ. I have made 4 offers to the owner of the sites that are in my niche and have a PR5 and are listed in DMOZ. These sites haven't been updated for a long time and I am hoping the contact email is still live and they accept my offer. http://www.techjaws.com/get-some-link-juice-as-geocities-plans-to-close/
The thing is... any GeoCities site that is of any value to it's owner will simply sign up to paid hosting at only $4.95 month... so what's your point?
Sometimes people do have valuable sites that they don't realize the value of. Or some people just wouldn't be willing to pay for hosting. So I agree that it could be a good opportunity.
Thanks for the update, and oddly enough geocities is one of the places that hides a few gems with regards to trafic and owners not knowing the value of it.