> To help with another post I tried -*
> +mime:text/html

MIME type filters, like size filters, can only work as additional filters ;
ie. links have to be scanned in the first place, because they depend on remote
headers (content-type, content-length ..).

In your case, "-*" excluded all links in the first place, leaving no links to
be filtered for mime checks.

What you can do is:
-* +*.www.thesite.com/* -*.gif -*.png -*.jpg +mime:text/html -mime:*

(first pass to filter obvious data, and second pass to abort download of
non-html data)