These days, it's pretty standard practice for an animated movie to cast all the major roles from the ranks of celebrities (i.e. the Lorax, where the few professional VAs are all relegated to supporting roles). And the occasional stunt-casting goes back pretty far (Boris Karloff as the Grinch, for instance, or Disney movies with some well-known singer playing the part of some character who carries a lot of the musical numbers). But can anyone think of an example prior to the 1980s Transformers Movie where they went all-in on celebrity-casting? Judd Nelson was a big box office draw at the time, plus you have high-name-recognition people like Eric Idle, Robert Stack, Leonard Nimoy and Orson Welles in the cast (alongside the regular VAs from the TV show).
Is there a prior example of a theatrical-release animated movie that went the Cavalcade Of Stars route like Transformers did?