A blacklist that can be added to anonymously and unaccountably is not something you want affecting search results.
You do realize spammers are extremely good generating large amounts of things, right?
> By getting a significant amount though and looking at each persons block list to normalize there blocks I think it would be useful.
Spammers are also very good (though not great) at adding innocuous data alongside their spam to look like real users.
You don't realize it, but your solution has just exploded in complexity.