AFAIK, the 1K/EXP/etc levels are not available for purchase, regardless of how close you came.
Again, AFAIK, AA counts ANY miles earned (even purchased or gifted) toward your lifetime miles (aka, LT Gld/Plt). A friend who is a Global Services with UA says that only BIS miles count toward your lifetime miles with UA.
I'm sure that someone here will correct me if I'm wrong in the above.