Thanks for the update, but I've run into a new issue (which either didn't show up immediately or went unnoticed
), wherein every time a Folder Action is invoked it causes Safari's tool and bookmarks bars to "flash," which I find unacceptable.
In addition, after giving the matter some thought I've realized that none of the solutions offered up so far deals with my situation... I
never use either Top Sites or Cover Flow, and rather than deleting Webpage Previews that have already been cached I prefer that they never be created in the first place.
So... I went back to Google and found
Disable Webpage Preview Images in Safari 4 Final, which is working like a dream in Safari 5.0.3.
To all who've kicked in, thanks, and to all who are waiting with baited breath, go for it!