It really depends on the person, however i would say outgoingness is definitely a plus. As a therapist, you must be aware of when is the appropriate time to show the right emotions. Your clients will be very different from each other, as all individuals are different. For example, I consider myself to be a very outgoing guy, however during class i am quiet, and only answer questions when asked.My level 1 fieldwork site, had a 2nd year student who was not "outgoing" and was more reserved. Despite this, she still managed to effectively build rapport with her clients. Personally speaking, i think the best term to describe a good OT would be a "people" person, someone who generally cares about people and likes to be around others. You don't have to be a outgoing to be a people person, you just have to be compassionate.