Hmm, haven't actually looked at the code for the audit tool.
Most likely I'll be able to work out the answer for myself after I've seen the code, but wouldn't it be possible to extend this tce.db to be something that the appbrowser updates when downloading a new extension, and the tce.db can then be added to .filetool.list, and thus greatly improve performance of the audit tool?
The current ability to completely rebuild the db obviously still included for when someone plays with their extensions directory by hand or doesn't include tce.db in their backups.