As a general rule, is taking Sus worth it for Castille?
It is a 1-base-tax province, but it produces gold, which is usually a good thing.
Taking it would mean taking ifna though, to connect it to the sea. This is another 1-tax province, producing fish.
TBH, Sus is the only reason I ever took anything in North Africa. It's quite valuable, IMHO, and Ifni when it cores is a good staging point for colonial ventures in South Africa, and then by extension India.
Edit: As a general rule, ignore base tax for overseas provinces. The tariffs and overseas modifiers will render them useless anyway.