Have you tried AECTOACAD or exporting it to 2007? Both basically do the same thing - they strip out all of the AEC junk and turn those "special" objects into blocks and plines... basic AutoCAD entities.
Give it a whirl!
Interesting. Exported it and then open the file and peform a quick save.
file size 12,809 kb = Before exporting the
file size 11,339 kb = after exporting but before opening the file
file size 12,557 kb = opening and saving the file
I bet my Arch Desktop put the AEC back into the exported file.