Maybe it's just me but I would prefer the "bonus material" to tie more into the stars rather than just being cartoons or shorts from the same period as the features. Myrna Loy, for example, made a ton of television appearances in the 1950's through the 1970's, it would have been wonderful had Warners tried to get the rights to a few of those as the bonus material. William Powell's career goes back to silent films - wouldn't have been great had they dug in to the archives and put a silent film or two as a bonus, especially since it's unlikely they will ever be released on DVD as a single release. And both Powell and Loy were all over radio in the 1940's, these performances would have been quite easy to locate and since most radio of the period is apparently public domain, added at little cost. Finally, why not add photo galleries of photographs of the stars (as well as movie scene stills) from studio archives, poster and pressbook reproductions, etc. This is material owned by the studio and wouldn't cost them anything other than work hours.
While I can see your wanting to see more bonus material based on the stars of the feature, I personally don't have a problem with how Warners currently picks it's bonus features. Warners, by far out performs most other distributors simply by adding bonus features at all. Fox offers very limited extras to it's releases (there are many Fox shorts from that era that probably will never be seen again) while Universal normally offers nothing more than a trailer or two (if you even get that). Getting back to Warners, I can appreciate the extras of a trailer or two, a short (normally from the same year the main feature was released), a cartoon (again from the same year) and occasionally a newsreel or radio program as well. After all, this is how these features were originally shown in theaters back in the 30's and 40's. It offers a complete movie-going experience to those who want it.