Favorite feature can be used for different purposes.
One of it's best usage is, when you see a question which might interest you but you don't know it's answer but would like to know if someone else answer's it now or in future, so you favorite it.
Now this question can be a good question and deserves a up vote or it might be not be.
What I normally do is, I favorite questions that I would like to know answer of in future and if question is good I up vote it too.
How to Programmatically change the text layout of a Sharepoint page?
I fav this question but didn't upvoted it as I wanted to know it's answer but I don't think it deserved "my up vote".
You can always view list of fav questions by going to your profile page.
How come marking a question as favorite doesn't automatically upvote
It's not necessary that every question you want to know answer of is a good question and has to be up voted (e.g. badly typed questions).