This, from Joseph Brooke, might help. I'm considering doing it.
"To address your first message there is the config option $originals_separate_storage - if you enable that in your ResourceSpace config.php file and then run the script pages/tools/filestore_separation.php it will split your filestore into two folders - "original" and "resized". Original uploaded resource files will be stored in the "original" folder while the preview files generated for that resource will be stored in the "resized" folder."
Jim