Lara,
My insight towards the subspecialty mirrors yours. The subspecialty is naturally competitive in the best programs. I agree with you that it is analogous to IM. I am unsure of the top endocrinology programs in the country because I based my applications on location (which was difficult cause I wanted to be in California only).
Fellowships, in general, are competitive because there are few positions. One of the programs I interviewed at had almost 100 applications and they interviewed 11 candidates for one position. I have been told during my interview season that there are now more IM graduates who are interested in sub-specializing than before, so the competition for fellowships has increased.
Endocrinology is not as popular as cards or GI probably because it does not pay as well. I am sure you know that any specialty that involves procedures pays better. When I started my residency, I realized that every specialty pays according to how hard you work and the hours you put in. I would never be envious of a cardiologist who makes $500K a year when I make my little $150K a year because I know he/she works much longer hours than me and has to wake up more times in the night (and not because of nocturia either!) than me.
I am not an endocrinologist (yet). One of the reasons I chose endocrinology was because I felt I would have less lawsuits. Being the chicken that I am, living in this litigious society, I figured that less procedures = less mistakes = less lawsuits. Also, I thought about how endocrine lab tests come back in absolute numbers that can help me decide on my next course of action. The decision to treat is easier to make compared to, say, a fuzzy lesion on an echocardiogram.
Patient compliance will be a problem no matter what specialty, but it becomes more prominent in specialties that have long-term patient-doctor relationships such as endocrinology. It used to annoy me when I started out as an intern, but now I just take it all in stride.
I think I have said more than I wanted to. It's great that you are already looking at subspecialties, because early preparation is so important. When I was in high school, I thought I was going to be a cardiothoracic surgeon. If you want more details on why I chose endocrinology, please send me a message.