With the current market, it is probably only profitable to fully restore the top tier of instruments with big name recognition, Steinway, Mason & Hamlin (in the U.S.) Bosendorfer. Perhaps some of the fine Europeans.
In the U. S. market, lesser known, but still fine pianos, like Chickering, Knabe, Sohmer, Baldwin can be restored, but probably not much of a profit. They are more often reconditioned and refinished. By that I mean broken parts replaced, actions regulated and worn springs replaced, hammers & shanks replaced, new damper felt, new pinblock, restrung. Fully restored is usually a new action and soundboard refinished with cracks shimmed at a minimum, more probably though a new soundboard too.
The older run of the mill grand probably would not be worth the price of even a recondition and refinish. They might make a fine instrument, but a craftsman would not do the work on spec (for sale) because he could not recover the cost of time & materials.
If you already own such a piano, you may be able to have this level of work done for less than the cost of a new grand of good quality, but I'd think the cost would approach that of a new good quality grand.
In uprights, the story is the same, but margins are tighter, so you'll only find a few fully rebuilt Steinway and Mason & Hamlin uprights.
Topic: It's cheaper to keep her...