That's pretty much been the case with every Woody-less Woody film in the last decade (or two). It's called the Woody Surrogate. What I understand is Woody himself encourages his actors NOT to do that, but they do it anyway. I guess it's like playing James Bond. Josh Brolin did it in You Will Meet a Tall Dark Stranger; Larry David did it in Whatever Works; Rebecca Hall in Vicky Cristina Barcelona; etc, etc.
Woody hits more than he misses (though when he misses, it can be excruciating... see: Another Woman on Netflix Instant), and Midnight in Paris is a definite hit. It's a fantastic movie, probably second behind The Skin I Live In for my favorite of 2011.
Brody was hilarious as Dali and the befuddled "Why can't they just leave the room?" question posed by Bunuel in regards to The Exterminating Angel was gold.
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"See that the men are thoroughly insulated, for we shall encounter extreme cold." - Dr. Zarkov