Finally I saved several hundred kilobytes.
It seems that the export scripts of Blender are more efficient than the plugin for AC3D. I was able to save about the half file size of some objects. The only case, where I kept the AC3D objects were objects with animation and objects where I had to use ATTR_no_blend (for example: trees objects).
All in all the whole package decreased in file size, so it's time to fill the gap with new additional objects. ;-)
