This is my current minimal-touch work-around for future searchers:
To hide the smileys from the editor (using the dokuwiki style), place this line in 'conf/userstyle.css' (or create the file if it's not already there):
button[title="Smileys"] { display: none; }
To stop conversion of text to smileys, blank 'conf/smileys.conf'.
Upgrading may break one or both of the above. If text begins converting to smileys again, just re-blank the smileys.conf file. If the smileys selector comes back, a more tricky workaround is required.
I would still like a nice option for this. Why are smileys part of the core distribution, anyway? They should be spun out into a plugin.