> If something does not go away after a full garbage collect, then it is 
> still referenced by something else. Here are some things you might try:
> 
>     http://minnow.cc.gatech.edu/squeak/2631


Great!! That did it. After closing all workspaces and doing:

Utilities emptyScrapsBook.
CommandHistory resetAllHistory.
Smalltalk garbageCollect.

... my image shrunk from 250 to 30 MB! What a difference!