Rub-n-buff is oil based, so it will weaken latex a bit.
Instead, you can take advantage of latex's tacky nature. As you unmold the piece, or after the final layer of latex has dried (depending on your technique), brush the surface down with metal powder (aluminum, brass, bronze, gun metal, whatever is appropriate). The entire surface will pick up a nice even coating. Buff it very lightly with a soft cloth and it will take a shine. Metal powders can be obtained from your local hobby shop. Wear a good quality dust mask while you use it.
If you are molding the pieces, you can also brush a thin layer of metal powder onto the mold before the latex is applied. The powder will generally stay more or less in place due to static electricity. It'll serve as a release agent, and help it to pick up a nice even layer.