I am describing a scenario where the spammer spams everyone they possibly can, en masse.

Any algorithm that tries to filter out the spammer’s notes based on checking if the spammer has been zapped enough time by “peers” would be fooled, because the spammer would have been zapped many times over (and it would look like other people zapped him). 

 Ok, i suggested an algo that works, your suggesting an algorithm that is broken and doesn’t. Don’t use that algo?

In my scenario, it would block a mass spammer because they would have to zap every single person they are spamming which would be very costly. 

 Isn’t your proposed algorithm susceptible to the exact same shortcoming of WoT then? ie. Nobody would be able to see new users. And even if these new users zapped you specifically, they’d still remain invisible to everybody else using the same algorithm. 

 I was only suggesting it in the context of a multi-faceted spam score algorithm. Zaps could whitelist a key so it doesn’t get accidentally marked as spam by other algos.