My personal opinion is looks dominate heavily in the beginning of a relationship, while it becomes less of an importance as time progresses. At first impressions, approximately all of it is based on looks. That's how they're gonna assess you. After a year or so, the spark dies and assuming the relationship still holds, it would tend to be bound more so by other factors such as trust, instead of the sexual lust present initially (not saying there isn't any left).
Also, I find that a good personality can make anyone more attractive. Sometimes I chat with a chick who is average looking, but my lust for them increases several fold after realising how much we have in common/how appealing their sense of humor is etc.
Similarly, I can get obsessed with an extremely attractive chick (i.e looks = 100%), talk with her, find out how much of an idiot she is and suddenly don't find her all that attractive.