The issue seems, to me, that a lot of these mental pictures are very personal.

I am reminded of an anecdote by Richard Feynman, from "The Pleasure of Finding Things Out". He explains how counting, for him, is a verbal process (he speaks the numbers to himself as he goes along), but that a friend of his would manage visually. (Text here)

He finishes by saying:

I often think about that, especially when I'm teaching some esoteric technique such as integrating Bessel functions. When I see equations, I see the letters in colors — I don't know why. As I'm talking, I see vague pictures of Bessel functions from Jahnke and Emde's book, with light-tan j's, slightly violet-bluish n's, and dark brown x's flying around. And I wonder what the hell it must look like to the students.

Because of this, I think there might not always be a significant value in trying to pass those mental pictures over - the real aim is to provoke the student into developing his own mental pictures, that he can strongly relate to. Some words such as "homological" or "homotopical" spark up very distinctive feelings in me, in a similar way as hearing "mountain" would make me visualise various mountains, hills, cliffs, etc. But whereas the meaning of "mountain" came to me through vision (mainly, but also other senses), the origin of my mental images of mathematical ideas comes through the practice of mathematics. As such, it seems harder to convey these mathematical pictures: they must be backed up by precise mathematical understanding, which at any rate should end up conjuring these mental pictures. Of course, many mental pictures are simple enough or "canonical" enough that one might imagine everyone would come to develop very similar ones upon understanding of one particular concept; the previously mentioned example of cyclic groups comes to mind. So there might be value in passing that on, but in the end I would think that understanding accompanied by the attention to what meaning it provides already goes a long way towards developing personal mental images.