All of that can be done in pure ASCII.
... that is, if you speak english. You can definitely write the way of
Shakespeare, but you have a tiny problem writing the way of Molière, let
alone Confucius. Then, there are things that are hard to do in writing,
however able is your prose. Maps and pictures, songs and recordings come to
mind. There was a rationale for creating MIME.
Framing the debate as ASCII versus HTML is a bit reductive. The real
separation here is self-contained versus network based. Carrying a picture
in a message is definitely valuable, carrying a link to a picture that is
stored on some random web site creates an obvious privacy risk -- the URL
itself can be the hidden communication channel that tracks you.