I think its more difficult to recreate or replicate a well-known thing, such as a Star Trek vessel, than it is to create a brand new ship. Why? First of all, the CAD program that is the shipbuilder is wonderful, but to make a very authentic looking Klingon cruiser,for example, is difficult because the pieces you have to work with are not exactly made for that purpose. Its a victory when you can make something like that and the rest of the community can recognize it.
Actors I think have a far harder time portraying well known historical or even contemporary individuals than completely new, fictional characters. That's because everybody has an expectation of what the real individual is like. I look at creating Star Wars, Star Trek, Babylon 5, Battlestar Galactica, etc ships the same way. The challenge is to make as authentic looking a ship as possible, and not have others (or even yourself) think that its lame.