In the end there is no perfect solution because the whole thing is gamed too much. Eventually spam sites will start paying popular users to like their spam page.
This attitude is too defeatist, and I'm not convinced. The OP's suggestion was that people would choose which other "favorite lists" or "indexes" they follow, this implies these are public. Who's going to follow someone who puts a StackOverflow clone filled with ads on their list? And if they do, and it shows in my results, I should be able to discover that someone I'm "following" has been compromised, and I'll unfollow them.