Ok here is the First kick at the can
https://github.com/thezenmonkey/SilverStripe-2.4-CleanAssets
It kept running into timeouts on DreamHost, but I just kept rerunning it until it was done, that seemed to work fine, Cleaned 800 files taking up over a 1GB down to 90 files. You need to be careful that you edit the code to handle your relations.
I also didn't do any parsing for $has_many relations as I didn't need it