So I'm a little late to this discussion (cramming for boards the past couple weeks). What I've noticed here is a lack of a response from someone who has actually done a combined residency, so this comes from someone who is a few weeks from finishing an EM/IM residency (and in other crazyness, just given a 10 year trophy from sdn forums)
Is doing a combined residency the best financial decision? Of course not. You know what else is a poor financial decision? Med school. As wide-eyed/naive as it sounds, there are some things that are worth more than money. For those of us who choose to do a combined residency and are proud of it, we can deal with not attending salary for a few years. We didn't pick an extended program for the money.
Since MS3 I wanted to practice emergency medicine. Internal medicine was not something that I found terribly interesting. That being said, I wanted to do EM/IM ever since I got to observe the very senior residents in my program. I thought they were badassess. Literally capable of handling every situation that could come up in the hospitals. Running floor codes like a boss, placing their own chest tubes while on floor services, extremely smart, extremely competent, excellent teachers. I looked at them and decided that that is what I wanted to be. Interestingly enough, my wife decided she felt the same way, so she is impending graduation along with me (and I can personally vouch for her badassness)
Hopefully, as a soon to be outgoing PGY5, I have managed to live up to their legacy. What I can say is that I'm proud of my program. We are known and well respected in our hospital system, and in the surrounding systems that we visit. I don't think a single one of us would resent the extra training we have, or debate that we feel it augments our abilities in both fields. A decent amount of us are going on to fellowship, others are taking their attending jobs. Some will be practicing in both specialties, some will stay with just one for now. Many former graduates work at our institution in both fields, and are leaders in the administrative and educational levels.
I happen to resent the implication that we are not capable of practicing competently in two specialties. This is not a new concept. There are plenty of EM-CC people out there who practice both fields. Surgeons can be intensivists. As Birdstrike is here to prove, an ER doctor can be a pain management physician. Does it require having an even more expansive knowledge base? Sure. Can we keep up with two fields? I'd say as long as you actually practice in both you would be able to. No, if you don't practice internal medicine for 20 years and then try to get back into it you are going to have significant difficulty, but if you keep your skills in each field fresh, we absolutely can do it. I will vouch for having rotated at various other institutions, that I would put one of our residents up against any others in the EM or IM fields and expect them to not only hold their own, but completely exceed all expectations.
In the end, I can really only give one opinion, my own, based on only one residency program. I don't know what I would be like today if I went somewhere else, in a more traditional residency. All I can say is, with residency finally coming to a close, it has been a long and difficult path, but one I have been immensely happy with. If I had to go back five years, I wouldn't change a thing. I can't say that it is the right decision for anyone else, only that it was the right decision for me.
If anyone ever has questions regarding combined residencies and/or my experiences or future plans, feel free to hit me up.