I think Eric hit the nail right on the head in saying that mansion is a character, of sorts. I think it's as much a character in Sunset as Norma, or Joe, or Betty is. It certainly added a great deal to the 2 performances I saw with Glen in L.A.
That's not to say that huge set is absolutely necessary for the show to work, but it is part of the reason THAT production worked so well. And no, I don't buy the argument that it worked well by concealing the show's flaws (or...distracting audiences long enough that they didn't notice). I'm not the type that sits there in a half coma, waiting to be *entertained*. Every flaw pointed out so far I noticed either while watching the show or the many times I've listening to it, but those flaws haven't taken away my ability to enjoy the piece as a whole. Not putting down those who found it lacking and mediocre as they have every right to feel differently and have explained why they feel the way they do. I just have a problem with the tired rationale of how the big set covered flaws and how some cheesy lyrics renders the whole thing a piece of crap.
Someone mentioned earlier that this show was criticized for its "literal" set design. Some of the sets were designed, I guess you could say, with a literal approach but not only is that approach valid for the stage, there was a perfectly logical purpose to doing this show that way, at least the landmark locales.
The Paramount gate; Schwabs; the Paramount sound stages, all of those are real life locales and part of the allure of including them in a production like Sunset Blvd., which also is a sort of homage to old Hollywood, is how well those are recreated. But that's just the historical settings.
I'd say Norma's mansion is the one piece that isn't done so literally. I love the obvious perspective tricks used as well as the overblown opulence, none of which are centered in reality. There is also a keen sense of loneliness that emanates from it. John Napier is a genius in the way he stirs just the right emotional response and infuses static elements with an essence that makes them feel alive. He did the same with Les Mis. He was less successful with Saigon but managed to create some visually haunting settings in that, too.
Then there's the manner in which his sets are incorporated and showcased in the story, which is as theatrical as one can get. The sets may have been more literal than most, but the delivery system was evocative in itself and served the storytelling effectively. In my memories of those two performances, I can't recall a single distracting scenic element. It all blended very well together and Sunset remains one of the most seamless productions I've ever seen.
Recreation of original John Cameron orchestration to "On My Own" by yours truly. Click player below to hear.