Much of the vocabulary in the poem in the OP
is casual and conventional, easily looked up.

I am having trouble, though, with "Schönheitskenner,"
obviously a compound word.
Of course I know that "Schönheit" is "beauty", "loveliness", and so forth.

Add "kenner" to it, and...?    Kennen is to know, have knowledge or expertise of.
So this is not, I think, a "Spiegel" -- a mirror, which is mere reflection.