While simple it is complicated. As we all know Rio Grande was an Argosy Pictures production released by Republic Pictures. Republic Pictures released the home versions until 1994 when Spelling Entertainment purchased Republic Pictures. In 1995 Spelling licensed the Republic films to Artisan Entertainment, which then released the films under their name. In 2000 Paramount purchased Spelling Entertainment and continued the licensing arrangement with Artisan. Now in 2003 Lionsgate purchased Artisan, and that is where the DVD rights reside.
Paramount did take back IT's A WONDERFUL LIFE and a couple of other Republic owned titles, but the John films stayed with Lionsgate.
With Lionsgate controlling the rights, the 2002 edition is the best to own. If there is another release, Lionsgate will more than likely just use the same transfer as the 2002 edition since they have gone that route in the past with other re-releases.
It is a great film and I actually like this one the best of the three John Ford "Calvary" films. You have good taste.