There's no doubt that the artist is the one who designs the furniture. There's lots of examples of "names" in furniture who rarely or never made the furniture but their name is the one associated with it (Stickley is an example). After all, many people can build good quality furniture, but designing something "new" is really, really difficult.
Regarding the "day in the shop", I really doubt if that makes much money for the shop. I think they do it more as PR and to get their name out than anything else.
Without Sam's signature on the furniture, people will not pay very much for that furniture. It's essentially the same as anyone else building a Maloof rocker look alike. Lots of people build them, but they don't get much when they try to sell it. People paid $25K for a Maloof rocker because it had Sam's signature on it, not because of anything to do with the rocker itself.
The Nakashima family had the same problem when George died.
Mike