I do think there's a certain level of similarity between the two. Although, a lot of the things they have in common are things they don't like about themselves. The negative self-image, the fear of failure, the lazy inertia... And I think those negative aspects of themselves and each other, are things they look at more than what postive qualities they have in common when dealing with each other.

One difference though, being that Xander can deal with not being the special one. Nobody really likes being a sidekick in someone else's life story, but Xander can deal with it. Xander is a team player, while Angel is a 'visionary' type and needs to be fulfilling his own direction to fulfill himself. Xander can be fulfilled by going with somebody else's.