The debate with no real answer is back again, as the lines of distinction--at least for golf courses, which are built of soil and covered in living, evolving ecology--are always going to be inherently gray. Our construction medium (sand/soil) is somewhat fluid and difficult to quantify. Rebuilding a mound to size/shape is not like re-instating a building's window that a plan once showed it to be 96 inches in height and 36 width. Furthermore, we are trying to restore 3 dimensional shapes to a grainy old 2-D photograph, trying to best guess at positioning, size, details, and the shapes and slopes behind the stuff you cannot see. Unless you are lucky enough to have the clues still on the ground, at the very least some of the finer details will inevitably be guess-work based on site conditions, seemingly obvious tie-ins, and understanding of the architect's other works and other features still present around the course.
So, assuming you have at least some photographic and/or on-the-ground evidence, it really comes down to intent and effort (and time allotted, but that also ties back into intent and effort, though perhaps moreso from the course/club themselves). How much does the original layout matter to those restoring? The bunker positions? The green contours and sizes? The mowing widths? The aesthetic details? The way the course plays? All questions asked in relation to that version of the course with that past designer you are trying to restore to. This is the big variable I see, with some restorations set on maximum effort towards the virtuous ideal of pure restoration, and some where the only effort is in how hard you are marketing and touting the word restoration. (And to be fair, not every old course should be fully restored.) The issue I think many have--me included--is when those projects do not really restore at all but then go on endlessly saying they did.
To circle back to the main crux of this version of the debate--agronomy--the main questions that should be asked are "do these conditions restore the shot-types from the original design?" In some cases, I would think they do. The contrast for me in playing my evening rounds at Pasatiempo between the two phases of front nine/back nine work was stark. In year one, with the "old" back nine still open, it was harder to hit certain running shots into greens and aim away from the hole, and almost every miss around the green meant a lofted wedge recovery. This past year, with the "new" front nine open, I was hitting all sorts of ground-influenced shots into greens, aiming away from holes to feed a ball in off slopes, and using almost every type of club around the greens. That last part is notable too in that I wasn't just using putter, as I am most wont to do, or wedge, as I was most forced to do on the prior version of the course. Between MacKenzie's side slopes, and the fresher, shorter, firmer turf around greens, the play was often to pitch it toward a certain part of a bank and work it back onto the green. For this you could use anything from a lofted wedge down to a 4 iron. It was a lot of fun, and in my opinion, even though this was fresh new ryegrass with fresh new bent greens, this aspect of the design had been "restored."
This isn't to say that many of the bigger high price tags are achieving this or even setting out to do so. Many are probably aesthetically driven, and some may even be about ego and braggadocio. Numbers, after all, are the simplest and easiest thing to argue about. But the more money you spend, the more scope you have to demo and meddle with something old and original, of which only the best intentions and most careful hands will work to preserve.