I think that sites really shouldn't have guidance on this sort of thing, because nobody would follow it anyway. If you only have upvotes and downvotes, people are just going to upvote stuff they like and downvote stuff they don't like, and any individual will have different rules about what "like" or "doesn't like" means to them.
Waaaaay back in the day, I did like how Slashdot had different categories for voting, e.g. "Insightful", "Funny", "Off topic", etc.