Celebrity is more or less orthogonal, I think.
Obviously being well-known is important, but it's about reputation more than anything. Zach has a reputation for have a strong creative hand in film and tv projects which have had a very strong connection with fans, as his work on Garden State has demonstrated. The same goes with the Veronica Mars team. Had Rob Thomas or Kristen Bell tried to use Kickstarter for some non-Veronica Mars related project they may not have received as much enthusiasm, because Veronica Mars as a project and as an entity on its own definitely has fans and definitely engenders a significant amount of trust that they'll deliver a product that is worth the investment.
Also, I don't think you have any concept of Zach Braff's reputation or following, and I suspect this project will probably exceed its goal faster than the Veronica Mars project did.