I think the differences between two persons could be attractive but however there are values very important which must be able to be share, for a successful relationship.

My former gf did. She broke it off because of it. I disagree. I think differences in opinion are only natural.

It depends on the views and how strongly they are felt. A similar value base is essential.

I think most of the time it's a recipe for disaster when two partners have mostly differing views. It's always an argument, and when it's not it's probably because you're holding back because you know it's going to turn into an argument. I think it breeds resentment and distance. Why bother? Is there really going to be a perceived benefit to broadening your views? Most likely not. It's not like it's going to be two people introducing new experience into each other's lives in terms of music or movie genres or foods etc. Ideologies are very different. They are the core of who we are and we become very defensive when they are challenged.

Both. There needs to be some common ground, probably in your more core values, to help you relate to each other. Then, differences in less crucial areas likely add some spice to keep things interesting.

The opposites attract idiom has consistently been shown to be incorrect however some differences are healthy i think as long as they don't become bones of contention within the relationship

I think more differences people have, the less likely they are to be compatible with each other.

There should definitely be similarities since those will most likely keep you two invested in the relationship, but having differences (as long as they are not extreme) are good too. Differences gives us opportunities to try new things that we might not have thought of doing by oneself. Plus, if your partner isn't interested in one or two of your interests, then having those interests that you can call your own and have some alone time every now and again is good for relationships too, imo.