Catalan here. There are historic and cultural reasons to split also.

The economic rationale behind your post is absolutely correct. However we don't want to split because we don't want to share; we want to split because of the missuse and economic opression and the unending corruption that plagues Spain. We don't think ourselves of so-prosperous at all in that sense - and at the same time I'll admit corruption is always an issue in democracy, but Spain's case is taking it to ridiculous levels.

Let me post sources in few for what I'm saying, on the phone right now.