Hi there, saw your post randomly, thought I would share my insights. RN/MD/DO/PhD, all are noble fields to go into. As long as you love what you do, you can't make a bad decision.
To be more realistic though, you do have to consider some practical aspects.
The MD, then the DO route is the hardest to pursue. I don't say that to disparage other disciplines, the numbers are there. You'll face the stiffest competition in terms of GPA, IQ, test scores, extracurricular humanitarian efforts, type A personalities, whatever else trying to get in to school. Then it's 80 hours + a week of studying or work for 4 years of med school and 3 to 7 years of residency working at the same rate. If you are interested in mental health, you will get the broadest and most intense training available, so long as you pick your training spots well (I compared notes with a PhD psychologist friend once...I saw as many patients in 1.5 months of my internship [~200+] as she did all year, and my patients were far more ill - dying, dead, bleeding, acutely psychotic, intoxicated, violent, manic, etc.).
Don't get caught up in the dichotomizing that some people do with psychiatrists doing meds and psychologists doing therapy. I trained at a top notch academic institution (I'm at another one now), and got solid CBT/ DBT/ Family therapy etc. As a physician, you have the most flexibility, highest pay, and your training will speak for itself (also, if you don't like psychiatry, you can switch to another residency...I considered dual boarding in internal medicine and psychiatry because I love medicine). A well trained physician (all aren't) can really provide true holistic care (medical, psychological, social, educational, etc.).
Regarding the flexibility you have as a physician, I see autistic kids/ fetal alcohol kids one half day, other developmentally delayed kids another, outpatient suburban kids, inner city kids at their inner city schools on another day, addicted teenagers, children ages 1-5, and rotate through other services at times (pediatric neurology, etc). The list goes on and on. I love it. I am just about to graduate after 6 years of training. The job market is fantastic (I got offered every position I even sniffed at), the pay is great, and the skills you develop with your training will speak for itself. You can really do what you want.
It's not all roses though. There is a cost to this. You have to think about things like "Do I want a family and kids (or do I want to see my kids while they are young)...Do I want to work most weekends a month and spend up to 30 or 36 hours at a time in a hospital...Do I want to give up the peak of my young adulthood doing things like standing in an emergency room at 3am with disheveled hair and coffee stains on my scrubs trying to manage a sick patient (funny but not kidding)?" I did internship (first year of residency) before the 80hour work rule. In one painful week, I worked three 36 hour shifts, back to back to back, AND a weekend day. Talk about delirium, but it made me a better clinician (so I tell my therapist, kidding). I am so happy that I chose to be a doctor, but someone asked me if I would do it again and I said, "only if you wipe out my memory for the past 10 years." 14 years of school/ training after high school (it would be more like 20 years if I averaged 40 hours all the way through) is a B%TCH, no way around it.
How about those huge student loans (some of my college buddies started working right after school, I will make alot more but they got a 10 year head start). The buck also stops with you which can be good or bad. Most of the therapists I work with get the "fun" cases whereas I end up with a large load of incredibly difficult patients that fall through the sieve of standard therapy and other medical clinics. Some of my colleagues who are family oriented partially regret their decision to do all the training, only to work part-time in the end. But if it is about having options, the MD route is the best, no question.
My wife is a nurse practitioner, master level. She works with kids too and loves her job. She is definitely bright enough to be a doctor (4.0 GPA in her masters program) but made a "life" decision to do what she does. She works with physicians on a high level and finds her work fulfilling. There is a shortage of nurses these days which has made the pay go up (good). It has also made them very powerful politically in the hospitals which sometimes leads to prioritizing work hours etc. instead of patient care. The thing about nursing that I couldn't handle as a control freak is just that, having control/ more autonomy.
As far as you original question regarding a niche for psychologists, I think the psychometric aspect of psychology is very unique to them in most respect and it is very important work. Psychologists are very dedicated professionals and are likely underpaid for the amount of training they have (my opinion). Social workers and licensed therapists can also do therapy but I usually have more productive and pointed conversations working with a psychologist on a difficult case (no disrespect to the other disciplines). Some of this is reflective of training, the rest is likely due to the median qualifications/ intelligence/ etc (more difficult training, more qualified applicants to start, that is on average...not politically correct but true, there are plenty of individual exceptions of course).
Psychologists can do a wide variety of jobs (forensics, psychometrics, therapy, nonclinical, etc). In the clinical setting, many psychologists can make very good academics (and all academics including MDs get paid poop so...).
If you enter the field of psychology, you will find a significant amount of territorial or turfy political goop. In a developmental disabilities clinic (autism, etc), there are sometimes behind the scenes political battles between psychologists, therapists, occupational therapists, and speech and language specialists about what they should and shouldn't do. You'll recognize and also sympathize with this turfiness if you work in academics. Even clinically, there are many opposing schools of thought or fiefdoms and some guard their therapeutic techniques like it is some kind of secret martial art (so says others, not me). PhDs and PsyD's are more varied in qualifications even amongst their own kind as compared to the difference between DOs and MDs.
I believe much of this turfiness and the psychologists' fervent guild related political activism is reflective of the sentiment you raised about niche, as well as their justified concerns about pay commensurate to level of training. So you definitely have a point. On the other hand, the hours are probably the most flexible in psychology compared to the other fields (no overnight call, 8-5 M-F, even in training!). People are well aware of this fact, and it is reflected in psychologists' demographics. 2/3 of graduating psychologists are women (which is good, but my personal hypothesis is that bright young women who wanted family and career who went to nursing school a generation prior, now go into law and psychology...hence the nursing shortage...okay maybe that's whacked, just speculating). One thing that is not good is that 94 to 95% of psychologists are caucasian, despite efforts to recruit minorities. Western psychology is of course heavily based on western values and mores. I think this will change with time, but it doesn't bode well in a public health model where diversity is currently the norm.
Sorry to ramble, man that was long! But my wife is watching this annoying dancing show, I already checked my fantasy baseball stats for the day, and this is fun. So in summary, I think psychologists are very aware of the niche issue but there are plenty of niche areas in the field. You should really find a career that suits your ambitions, work ethic, tolerance for suffering (ha), and most importantly LIFE goals. What do you want to say you did when you are 65 and retired?
