It can be a hard line to walk that one, but in principle I do agree with you. Sometime's it's neccesary to use a certain term to show a subtly of meaning in a context, but from what I know 'Nakama' is not one of those.
I mean, I'm currently writing Yu-Gi-Oh fanfic, and because of the genre I sometimes use 'Nii Sama,' and 'Aibou,' because in both contexts it's kinda important and it's very heavily recognised in fandom, but that and the occasional honoriffic is about as far as I go.
In general it can be a bit of a difficult line, but I thik the less the better as a rule and Nakama isn't so special a word that it can't have a translation. All langauge carries with it a subtly of meaning, if you're going to argue against every case like Nakama you might as well not bother translating it at all.