The Z31 retained many peculiarities of the previous 280ZX. The super-squatty rear suspension, the whole "GT" vibe, Tokyo fab interior electronics including optional voice system. I had a few Z31's whilst my friends had 280ZX's, the 2 cars felt/appeared remarkably similar. We also had a Z32 amongst our friends, and that car was completely different, felt totally "clean-sheet".
The only thing a Z32 has in common with a Z31 is it is a "3.0 V6" even though it's not the same engines.
I'll defer to your experience, but I was mostly talking about first-impression visual design cues, rather than mechanical differences or similarities. I was talking about the overall look that is plainly obvious from the first advertisement image, before even considering deeper analysis.
280ZX shared many design cues with the S30 Z cars before it... from pocketed headlights on either side of hood long enough for an I6 engine, to the forward-peaked roofline, and a distinctive C-pillar, rear fender arch, to a Kamm style tail, and stacked horizontal bars as rear lighting. S130 was an evolution.
Z31 was absolutely not an evolution of what came before it, stylistically, just as MA60 Supra looked very different than it's predecessor, and Fox Mustang looked nothing like any of the previous Mustangs, and even C4 Corvette lost it's Coke Bottle curves from the C3.
Z32 was mechanically much improved, and had a much nicer interior, no dispute there... and not much of a styling evolution from Z31, but it kept the flat slant-nose with aero headlights in leu of aero pop-up headlights, and was a second successive styling renovation that was not an evolution...
but it wasn't the first styling departure from the classic Z visual traits, and by not being the first design departure, but rather the second iterative departure, Z32 doesn't seem as stark of a break from preceding tradition, even though Z32 is clearly a very positive design change, and one of the best looking cars of the modern era, let alone the Z lineage.
Just as Mark III Supra is a better looking car than Mark II... Mark II was a much more stark difference from Mark I, and Fox Mustang was the biggest stylistic departure from tradition in Mustang's History.
Most people would probably consider S130 280ZX, Z31, and Z32 as cars that skirt the line between sports cars and Grand Touring cars, especially with 2+2 versions and increased amenities at the expense of weight... where cars like RX7 remained smaller and lighter.
Z33 was when it came back to a sports car format, where G35 took the GT role on the shared platform, and was the better looking car, IMHO. I wished the 350Z had looked even more like a 2-seat 3-door G35, and didn't like that 370Z went the wrong way stylistically. Somewhere between Z32 300ZX and G35 coupe would be a point of auto design nirvana.
The Z33, Z34, and now Z35 are all designed with some measure of retro cues to classic Z cars, and are not complete clean-sheet styling, the way the 1980s cars were. Just as SN-95 to current day Mustangs, Camaros, modern Beetles, SSR, HHR, Thunderbird, Prowler, Charger, Challenger... and on, and on, and on, and on.... all look to the past for design lineage as well as their nameplates, rather than clean-sheet originality.
A completely new design is much harder to pull off successfully. Original designs have a much higher risk of being rejected if they are controversial, especially with a nameplate that has tradition behind it. Nissan doesn't have a great track record with original design. I still blame Juke for a lot of 21st century ugly car design. Catfish Maxima was not great, either... 370Z, Cube, outgoing Pathfinder... and the horror of Murano CrossCabriolet...