One such example is the retro Kawasaki 900's currently produced that are based on the Z900. Having owned a '73 original Z1 and ridden the new one that looks almost exactly like my root beer and orange version from back then, it's kind of the best of both worlds if you're into that. Not that much different from cars like the new generation Ford Mustangs, Camaros, Challengers, etc.
IMHO, looking the part is not quite enough, and the Z900RS, while I think it looks great, IMHO misses the mark just a bit. I wouldn't kick one out of my garage but I really prefer my air-cooled Bonneville. I agree BTW about these new Mustangs, Camaros, Challengers. They tap into the appeal of nostalgia due to appearance. But they really miss the point IMHO.
But the point is, there's nostalgia, which is one thing. Nostalgia in this case, to me, is kind of like, "I like it because it reminds me of something old". But there's something more than nostalgia that new motorcycles can tap into. There's something timeless about certain things that goes beyond appearance but is much more about some characteristics that give them personality or character making them beloved across all time. It's not just how it looks, or really how it feels, but about how it makes people feel about it. Nostalgia, to me, is about making you feel young. But there can be more to it than this.
Example among cars is when I first test drove a NA Miata, at the time my daily driver was a 1972 240Z. The Miata didn't look like a Z at all, but it totally captured a lot of what makes you love a 240Z. And the 240Z shared these characteristics with an MGB. My NB Miata was very close. It had the great characteristics of a 240Z but with 4 wheel disc brakes, fuel injection, a 5-speed, 100K mile between service kind of reliability, and a top that could go down.
There's a trick to designing a modern thing that captures the character of old things that made them great. I think Triumph did it just right with the 865cc EFI air cooled Bonnevilles. I think it's possible that Honda did it with the CB1100 redux. Royal Enfield seems to have hit the mark with their 650s. Kawasaki even did it with the W650/800. Genuine of course did this with a Stella, since it's basically unchanged from the original. And Harley has probably done a good job of this with many models even though they don't appeal to me. I think the Z900RS, Ducati Scrambler, Yamaha XSR700/900, etc. all seem more like modern bikes playing dress up as a retro, which taps into nostalgia for sure, but doesn't really do the trick of capturing the je ne sais quois that made the old ones great.
IMHO of course. I know nostalgia is super valuable. I was only a wee tot when these original motorcycles were made so nostalgia doesn't mean much to me. But I have a strong appreciation for the classic formula of great machines.