I did Spanish up to AS, and really enjoyed it. I did then drop it, and had always intended to drop it at the end of AS.
I found it really useful. While it is a big step up from GCSE, the way I was taught was good, with a good focus on grammar. Obviously I don't know how your school teaches it, but you need to really understand the grammar. GCSE is nice, but not that helpful in terms of preparing you to go and use your spanish abroad. While I'm by no means fluent, I have sufficient level to communicate enough with native speakers to make myself understood. Admittedly my listening skills aren't as good, and don't always understand their responses, but I can usually get the gist of it!
Psychology may be nice, but Spanish, I believe, is more useful!