That massive purge sure didn't get rid of a lot, did it?
Dino: RCZ.dwg (1535.2 KB - downloaded 2 times.)
Mine: RCZ.dwg (1524.76 KB - downloaded 0 times.)
Just for grins, I tried a purge and got no change at all. Then I saved the file and it grew larger.
The thing only has 38 polylines in it on one layer - I don't know what is taking up the space.
There must be something wrong in translating to the old formats, 2006 opens it with no problems.