Actually, for Psychology undergraduate courses, research rating is of the utmost importance. For most subjects it isn't, but for Psychology it is. Undergraduate students take part in most of the current research, by volunteering posts, statistics teaching, lab teaching, or participation schemes where the student must have participated in enough experiments to pass the year.
They are taught how to conduct research by learning from the current departmental research (which is why the content of the degree will vary from year to year in the research side of it). Learning how to conduct Psychological research is integral to the degree, and can only be taught in this way.
It may even be fair to say a bad research department = a bad Psychology degree.
I take it you're not a Psychology student? Because most would know the research quality of the department is absolutely important.