I did AP/CP before FP, and have to look up things from time to time too. The board certification, per se, is pretty much irrelevant as far as actual practice goes. It has no bearing on qualification as an expert in FP, though I could see it possibly brought up as a comparator to the other side's expert in civil litigation -- which in my experience is a minor to non-existant component of the average FP's trial experience (with the exception of a few who just do consulting). But just because a thing might be brought up doesn't make it meaningful.
I do think there is value in some CP training for those who are going into FP, but that's different from saying one should become CP certified. The strange thing is that one of the reasons I wanted to go ahead and get CP was so I could better argue at some point down the road that anyone doing FP *should* also do CP -- because it is valuable by adding to one's foundation, and is relevant to common issues in FP such as toxicology. I guess the view of a young and impractical idealist. However the ABP combined with rising costs of medical education and very limited increases in FP salaries has made that a difficult stance to continue to support without looking like an impractical idiot. The ABP says working solely as a subspecialist has no value, and if you don't go back and study or practice general AP/CP then you shouldn't keep your boards at all (nevermind that some subspecialists don't have to do general AP or CP to begin with.. these aren't the droids you're looking for). And FP training can fill in those gaps or weak foundations in what are otherwise generally considered the realm of CP -- tox, micro, etc.
What you really have to decide is whether 1 extra year at a resident salary is worth the additional foundation in things you will STILL most likely have to look up when the rare case comes along that you want it, and whether you want to be forced to maintain it (it's own problem with requirements that can, and will, continue to change).
