Does completing a thesis make you a better practicing psychologist? I am a strong believer in the importance of the scientist-practitioner model for psychology. I think that training in the scientific method is a major component of what makes a person trained in psychology more employable.

In many jurisdictions, a student wanting to be registered as a psychologists is required to complete one more research theses. For example, in Australia, a student will typically complete an undergraduate fourth year thesis and a thesis as part of a larger masters or doctoral program.
While it is obvious that training in research will make a student a better researcher, I have heard some people question whether completing a research thesis will make the student a better practising psychologist.

Thus, my questions are:


What empirical research exists that has tested whether completing a research thesis in psychology makes you a better practising psychologist?
What theoretical frameworks justify or challenge the value of completing a research thesis in terms of improving practical skills required by a psychologist?
You might want to study differences in PsyD and PhD clinical psychologists.  The thesis per se doesn't seem to be the question but the focus on research.  A PsyD dissertation generally does not involve the conducting of an original line of research while the PhD does.  I can't think of a better way to equate your groups at the moment.

As a comment I'd like to mention that the benefits of a scientist-practitioner model reach beyond the immediate and are best seen long term, as the practice of psychology evolves.  Someone trained only in therapeutic techniques is trained in a stagnant psychology and is ill equipped to understand new research that motivates changes in the field.  They may change but the decision to won't be as well grounded in science and will be more based on their clinical judgment.  

If you've ever been to a clinical conference where the budding field of clinical neuroscience was endorsed by a speaker through a careful presentation of (astoundingly powerful) research and logical argument you'd see an embarrassing number of practitioners making serious scientific errors dismissing the idea.  And it's not just a bias against new but an inability to make sound scientific judgments.  The ridiculous case of Autism and vaccines and how many psychologists actually endorsed that research highlights how we need better scientific training.  A training that many an experienced scientist can tell you really only comes through practice.

If you come up with a better way to produce a clinician on the day after they graduate then you haven't necessarily come up with a better way to train a psychologist.