(This post is probably too late but...)
Smurfs as stated is definitely aimed towards the younger/family crowd and will probably bring in more $ to your theater. Some people will be going for the nostalgia factor but even that won't get me to go watch it. I was really unimpressed with the trailer, CG, the jokes, and what's-his-face,...Everything seems sub-par to the original series in my opinion.
Cowboys & Aliens is aimed at a totally different audience that includes, I would assume, the teen-and-up crowd. And with this film some of your audience may be well aware of film genre conventions (Western/Sci-fi/Disaster/etc) and how they are related and different... Anyways... without getting too detailed if I had a movie theater I would be showing Cowboys & Aliens opposed to Smurfs tonight. I'm more interested in film theory/experience than what I am in a let-down flick with the potential to score some money.
I'm going to see Cowboys & Aliens tonight at the local Drive-In. (: