I've been through sanding/no-sanding thing a few times now. My recommendation is, if you want to preserve the petina or use a historically accurate finish, then do not sand. If you don't care about preserving the historical finish, definately sand. Even a light sanding will bring out fresher grain & wood color, which will look much better on the finished product.
A handy trick is to use steam to remove cosmo from an old stock, useful even if you decide not to sand. Some people use steam guns, I just use a soaking wet cloth and an old cloths iron. A few seconds of moving contact with the wet cloth in between the iron & wood just sucks the cosmo and hand grease out of the wood and into the cloth. It also apparently helps lift any depressed knicks, etc in the wood.