I own and use both a vintage S3 and an S3-2000. The metal on the top plate and face plate seems to be of a slightly different type on the new one. I switched the face plates on the two cameras, and they seemed about the same weight and density. I used the vintage S3 professionally for more than a decade, and it had a dented top plate before I even got it.My SP also has dents. So I think the old cameras can dent, too. For the most part, the build on the cameras seems nearly identical. The vintage S3 has a kind of smooth "broken in" old car feel, especially on the shutter advance, whereas the new camera just feels very new. I've had the old camera apart, and it's got a lot of greasy gunk in that probably helps with that broken-in smooth feelling. I've owned the vintage S3 since 1989 and have run thousands of rolls through it. I've owned the S3-2000 for about a year and have run about 50rolls through it. I don't shoot newspaper work any more, so it doesn't get knocked around like the vintage S3, but I still travel often and carry it as my daily camera. The finder of the vintage S3 has not aged badly at all. In fact, the new and vintage finders are nearly identically bright. My S2 is also bright. The SP is the only Nikon whose finder doesn't age well. (I'm in the minority of Nikon RF users who prefers the S3 over the SP -- I love the S3's enormous bright finder).
I've also done a considerable amount of newspaper work using the 50mm lens from the 1960s/early 70s (I own two chrome-barrel ones that I AI'd and have used all the way up to digital bodies). My sense is that the Millenneum 50mm lens lens that comes with the S3-2000 is at least as good as the 60s SLR lens, probably better. It has better coatings. It seems to produce richer images.
Here's an earlier thread on this lens.
I disagree with the small number of people who recently claimed the 50mm Millenneum lens is too contrasty. I think that's mainly a subjective Leitz versus Nikkor thing. Letiz lenses have always had less contrast. Someone with thousands of dollars worth of Leitz gear is going to be attuned to that level of contrast. yet that's also a typical buyer for the Nikon S3-2000, and they suddenly find themselves with a camera with backwards controls and a lens with a different look and feel -- not better or worse, just different. I've got thousands of dollars worth of Nikon gear and am attuned to Nikon's level of contrast. As an ex-newspaper photographer, I like contrast and used to do most of my B&W printing on #4 and #5 paper. So there's a good chance I would consider the Leitz glass to be too flat. But, unless you're shooting slide film, contrast is something that can be modified in the darkroom or on the computer.
EDIT: Film choice also has a huge effect on contrast.
Attaching a couple of recent photos taken with the S3-2000 and 50mm Millenneum lens.
Nikon S2, S3, S3-2000, SP, SP-2005 / Kiev 2a
Biogon 21/4.5; CV 21/4; CV 25/4; CV 85/3.5; the following Nikkors: 2.8cm/3.5; 3.5cm/1.8 (1956 and 2005 versions); 5cm/1.4; 8.5cm/2; 10.5cm/2.5; 13.5cm/3.5
Soviet lenses: Orion 28/6; Jupiter-12 35/2.8; Helios-103 50/1.8; Jupiter-8 50/2