I agree with you on Girl Happy and Speedway. Shelley Fabares and Nancy Sinatra both respectively add much to the enjoyment of those films. I might throw in Kissin' Cousins too if only because of Yvonne Craig and a good title song, although the DVD is probably fine enough.From Elvis Presley's filmography I think Warner can only release his work from MGM, Allied Artists, United Artists, and National General Pictures. They don't have the rights to his 20th Century Fox, Paramount or Universal titles.
This doesn't make his best films available, that are not on already on BluRay.
I'm pretty sure that Jailhouse Rock, Viva Las Vegas and his two concert documentaries; Elvis That's The Way It Is and Elvis On Tour will make it to 4k eventually, until then the BluRays will suffice. With the docs will they go to the expense of scanning all the unused footage (several hours of it) sitting in the vaults? Probably not. Warner Archive has released It Happened at the World's Fair on BluRay last year. Follow That Dream and Kid Galahad were on BluRay already as are three of his weakest; Tickle Me, Frankie and Johnny and Clambake.
So what does that leave WA to choose from when deciding, besides Spinout?
Kissin Cousins, Girl Happy, Harum Scarum, Double Trouble, Stay Away Joe, Speedway, Live a Little Love a Little, Charro and The Trouble With Girls. From that list there are two fun, average Elvis musicals that i hope the Archive does release - Girl Happy and Speedway, a OK comedy in Live a Little, Love a little and a curiosity piece that has a nice feeling for it's period setting (The Trouble With Girls). The other 5, DVD was good enough.