1. After searching the source for any occurrence for the string "0.2.0" and not finding a single occurrence, I've removed the folder ace-0.2.0 on our local install and haven't noticed any lack of functionality yet. Saved: 7.56MB.
2. I had previously already removed the demo, kitchen sink etc. folders to similar effect: no loss of functionality, but major savings in disk space. Saved: +10MB if I remember correctly.
3. I would also suspect that js/jquery-ui-1.8.20.custom.min.js might not be needed anymore when having jquery-ui-1.9.2.custom.min.js. Saved: 178kB.
4. js/autocomplete.php.js and js/autocomplete.wordpress.js are unused duplicates of files under js/autocomplete folder. Saved: 1.28MB.
Our installation of version 2.3.2 of the plugin now takes 8.55MB. Default install takes 34.4MB. So far we've been able to reduce the plugin size by 75% without any loss of functionality by removing leftover files.
5. Removing the git folder saved another 1.26MB. Based on comments in the code the support is experimental, and I wasn't able to see any way in the user interface for making use of this, so removing this hasn't revealed any loss of functionality either. Trimmed plugin size: 7.29MB. Savings: 27.11MB (79%).
Simon: hopefully this helps you in some way :)