Brillyant's comment above basically gives the answer to this: beauty doesn't provide as much long-term happiness as the ICVPI facotrs (individual character, values, preferences, and interests).

Do you have any research to back this up?

Intuitively, of course, it's easy to see how a relationship would suffer for a lack of these things. But on the other hand, data on relationships where the partners don't find each other at all attractive is limited as such relationships tend not to form in the first place, although no longer finding each other attractive is a commonly cited reason for relationships ending, which suggests that it counts for quite a lot for many couples.