It's not scriptable in Acrobat except by executing the menu item.
Thanks for confirming that.
It's such an obvious use case that I guess Adobe must not want Acrobat Pro being used where Acrobat Server could be sold. Oh well. I'd use multivalent or pdftk, but neither offer image re-sampling or attachment stripping at the moment.
This limitation means users have to babysit the script a bit, which is unfortunate, but not the end of the world.
I think a batch process can do this automatically (if you have Acrobat Pro,