Personally I find those inset medicine cabinets are not very useful at all. Our one home came with one, so I kept it, but really limited to what can go in there. My friend turned her cabinet around (if you can follow this) so the door opened onto her face as opposed to the wall. She uses it for makeup/contact lense application. I thought it was a v good idea. But to answer your question, it wouldn't hurt resale especially when you have a 2nd one.

Weird, unusable details can affect sales. Provisions for appliances sounds like a good, up-to-date idea, especially if attention is paid to creating a convenient power source,too.