Why not Tom Selleck?  He's presentable, articulate, committed to RKBA.  Besides, If you were on the fence, who would you listen to in a debate, Sarah (cough) Brady, or Mr Selleck?

Well, if Selleck can't/won't run, how about Susan Howard, for the exact same reasons.  I once heard her give Clinton what-for during a TV show.

Just why does it have to be a celebrity? Once is one thing.. but a pattern of it will diminish to some respect the legitimacy of the organization, making it look like we are only out for publicity.

You don't see the VPC nominating Rosie to lead them.

Celebs, in the rare cases that have actual intellects and core values, are used to being before the camera, performing their duty under the same kind of pressure they will face from the press, and Rosie excepted, more likely to be looked at and paid attention to because of their good looks.  It's a tactic to get out the message.
Ultimately, though, looks aren't enough.  Their head and heart have to be in the right place first.
In response, who would willingly look at Rosie for long, let alone listen to her, besides, she's an airhead.
To turn your question around, why not continue with a winning formula?