Attention Bonds
wiki.asrg.sp.am
wiki.asrg.sp.am
Not to mention if the value imparted is informational, once you read the email (to judge whether spam) the value has already transferred, making it easy to double-collect by hitting spam.
I think this is the most important point of the whole concept. Make people pony up cash to send email, and they will send their messages in some other way.
Remember when SMS messages used to cost money no matter what service you used?
I'd say that in that limited scope of an example, opinion polls and consumer action were very similar.
Also note the myriad issues associated with mailing lists and similar.
But there's still a very large cost to systems, sysadmins, etc. - because all of that spam still gets sent, so processors still have to devote cycles to sending it, receiving it, and classifying it, and someone pays for the bandwidth as well.
Attention bonds would combine perfectly with cryptocurrencies to provide a general basis for contracts. Perhaps it could make for an honest ad business!