I disagree/would add a few things to what WisNeuro said above.
1) Yes, absolutely. Even if it didn't turn into a poster or publication, because you might not have found anything but that doesn't mean the study wasnt good. I love to see senior theses/honors theses, particularly experimental ones, because it means the person has at least SOME idea of what doing a study and writing it up entails.
2/3) I personally don't care as much about research area as quality of research, as WisNeuro said. What I'll add, though, is that you can spin just about anything in your personal statement. If you choose a physio/neuro lab but you want to study mood/personality disorders, you can talk about how the methodology you learned could be used in X, Y, Z ways in the area you area really interested in, etc. You want to get research experience that will be substantial, AND where the person mentoring you will be able to know you and write you a good letter. Unless the writer is uber famous, think more about what the writer can say than what type of research it is.
5) Some PIs might care, but I suspect most do not. Having no clinical experience is fine in my book. The only thing I find valuable about clinical training like crisis hotline training (or other kind of medical experience, like paramedic training or something) would be some indication that the student might be able to handle strong emotional situations, and isn't really scared of them. But other than that....don't care. And, in fact, someone with a LOT of clinical training might actually get discounted as being "too clinically focused" which could turn some PIs off.