Steve Miller asks about "middling", "never more than average", or "disposable" pianos.
This is a subject that is based directly on the history of the market for pianos in general and the number of really good high end pianos in particular as well as new vs. used pianos.
At one time, around the turn of the last century, a piano was something like a TV with an attached VCR or DVD player. A piano provided a family, usually a rural family, with basic entertainment. Previous to that time, the piano developed along with the music and musicians that wrote music for it beginning in the late 18th century when the piano took the place of the older harpsichord. It took about half a century for the piano to develop into the instrument we know today. Along the way, production increased and prices fell relative to other products. More people wanted them and more of them were made. More of them were made cheaply than with a lot of care, middling, never intended to play or sound very well. By the early 20th century, piano production was the highest it had ever been and more pianos of all kinds were being sold than ever before. Some great instruments were made back then, the golden age grands and large uprights, and a lot of junk was made too, cheap uprights, and the cheapest baby grands. A lot of player pianos, both grands and uprights were made too in all kinds of qualities from fairly high end to downright junk. During the 1920s, the piano business was facing the pressure from the radio and the phonograph and shrinking.
Then 1929 came along and the world economy went into the Great Depression from which it didn't fully recover until after World War II. The piano business shrank dramatically, many companies went under. The better or more widely recognized labels were bought up and fewer quantities were made in consolidated factories. What were the surviving piano makers to do to keep going? What if someone wanted a new piano but had an old one they wanted to trade in? Pianos were taken in trade and destroyed by the thousands during the 1930's, by far the most of these were the cheapest and least desirable pianos. People frequently have the idea that their grandma's no name upright was really worth a lot of money when the truth is that most of them only cost a few hundred dollars when brand new and are worth exactly less than that now.
There are other factors at work now too. The upright piano is in some serious trouble, at least in this country. Most people would prefer to have a grand, so much so that they are willing to buy something that is really too short to be even as good as the best tall uprights. There is a sense that if not a grand then maybe an electronic keyboard that might at least be portable. Uprights make a lot more economic sense than grands only when the customer really wants and needs a real piano.
Another factor is the culture. Where is it? Oh, it's there, but it's greatly diminished and spread out. We are currently living in a fundamentally unmusical age. It's not that the music, where and when you find it, isn't as great as previous epochs, it is frequently better, it's just that there's so much less of it compared with fifty or a hundred years ago. We must recognize that entertainment takes time and that time is limited. It's getting harder all the time to justify entertainment with the level of application and downright hard work required to play a piano well. Fewer people are devoting themselves to it. The high end pianos out there seem as plentiful as they've ever been but the prices have risen along with everything else.
There is a special niche for a few really well done rebuilt pianos. These are frequently pianos that were above average when they were made and can be turned into instruments that are frequently far better than their original designers ever intended, including those that were high end pianos back then. We're talking about a limited number of grand pianos made by no more than 25 or 30 makers at the most that fall into a period of time from no earlier than about 1875 through 1929.
What is it about a piano that makes it "middling?" Shoddy materials, cutting corners structurally, inadequate or substandard scaling including faulty strike points, poor design intended to make the piano easier to manufacture. Any of these things can make a piano an unworthy candidate for a rebuild. Action design was pretty much stabilized by the end of the last century, but there were always some makers that thought they had a better idea or a way to make the actions cheaper.
I hope this gives Steve and others some idea of the basis in fact for a piano being less than what it could be, to own, to maintain, to play, glory in or ultimately to rebuild.
The only reason I can think of that Asian pianos aren't considered worthy rebuild candidates is that there aren't enough of them that have been around long enough. Let's take for example a Yamaha grand at least the size of a C2. What would happen if we decided to rip it apart, put a full fit pinblock in it, put a soundboard in it that was made of the best Northeast white spruce and designed to have a crown built into it rather than having the crown compressed into it. Let's also suggest that the soundboard could be adjusted from underneath by the rebuilder after installation to get the best placement of the piano's crown for the best projection. Let's further suggest that the scaling was redone to improve the tenor section and the break and the bass strings were made by a real master like Sanderson or Isaac. Let's suggest that Steinway, Abel or Renner hammers were used. I happen to like Isaac hammers real well too. You're going to end up with a far different sounding instrument than a typical Yamaha.