I wish the Oscars wouldn't waste their precious best picture nominations (although admittedly it's expanding) with films that are solely based around the basis of one performance.
I would put Erin Brockovitch, Ray, Capote and arguably The Queen in this category as well as My Left Foot, Shine and Tender Mercies.
Just as we decide the basketball MVP by taking into account the effect of one team without that player vs. the team with the player a strong film is one that I would define as engaging outside of the performance of one actor. That's what acting categories are for. Giving a film a best picture nomination as a way to secure it a place in history and ensure that many movie buffs will check out that film because it's been recommended as one of the five films of the year. The above-mentioned films already get their place in film history because people want to check out the best actor performances in these films. So if these films are not up to par, it's just a waste.
Ray would still be a strong movie if Ray Charles weren't in it: The film certainly does a good job at positioning Ray's life within the context of history and the ups and downs of the story had a certain emotional resonance. However, if you replace Jamie Foxx with a slightly less capable actor, the film would have probably dropped to 7th or 8th in the best picture voting behind "Hotel Rwanda" or "Eternal Sunshine of the Spotless Mind".
Erin Brockovitch was an especially unnecessary choice with Soderbergh already getting a nom for Traffic that year. Ask yourself if the film's very existence is even justified without Julia Robert's performance. That was probably the pitch to the studio: Julia Roberts as a skanky, poor and plucky legal assistant, it's Oscar Gold. I would have recommended Oh Brother Where Art Thou, Contender, 13 Days or Almost Famous in its place.
Capote is what I consider to be the worst best picture nomination of the decade. The premise itself of exploring a fish-out-of-water flamboyant urban gay writer in the heartland of America finding himself in the middle of a murder case is gold. But Capote never capitalized on this nearly enough. In fact, a better film with the exact same story came out the year after and it had better performances and lead films. Constant Gardener, History of Violence, New World, Match Point, Walk the Line (which boasted not one but two great lead performances) and Syrianna would have all been better choices.
The Queen is arguable since it's an astute look at politics behind the scenes but would it have lost enough stature to Dreamgirls or Pan's Labyrinth had Mirren not been such a revelation in the film?