Two things I do in that situation.. first Purge RegApps
_-purge
R
etc........
2nd
If I have access to autocad 2014 I open with that, and then use
_-exporttoautocad
set the format to 2010
Bind set to "not bind"
Suffex to "2010"
then ent ent ent to save.
it will then save yourfile.dwg to the file yourfile2010.dwg and it will include the layout as well as model space.
this has the effect of removing any types of items like ARX objects that can cause files to bloat...
If you can give that a shot. and report back that would be awesome.