Are studies published in conference proceedings well-regarded in social sciences fields (e.g., psychology)?
I have worked at the intersection of psychology, educational sciences and computer sciences and there was always friction between the computer scientists who wanted to publish in conferences and the non-computer scientists who wanted to publish in journals. I think most psychologists who deal with computer scientists know about the conference culture, and most computer scientists that deal with psychologists know about the journal culture. That said, I believe, it is much easier for a computer scientist to get an idea about how competitive a journal is compared to a psychologist trying to understand how competitive a conference proceeding is. 

If your plan is to stay in Psychology and you have the choice about conference or journal publications, then all things being equal, go with journal publications. If you want to go to the conference or you are getting pressure to publish in conference proceedings, then it is no big deal, although, there are even differences between conference proceedings and journals in computer science so you probably want to prove you can write/publish a full article.