I am not very far along with my voice MtF, and probably only a vocal coach would have experience to base an opinion on. My thought is that becoming aware of how your voice is being produced, feeling it and being able to control it is what is required to change one's voice, whether it is conscious or not. So, learning to change one's accent is experience that can help to become familiar with how ones voice is produced. That would mean that it could be a less than optimal use of one's time, but wouldn't hurt unless it requires extra time and you become discouraged because of that.
If you have difficulty producing the farmer's daughter's voice, then trying a different accent seems to me to be similar to advice like "imitate a valley girl": barf me out, totally, etc.
For AmyBerlin, I find female German accents attractive. But, I know what you mean about it not being easy to base a modulated feminine voice on.