all of these renders seem to be struggling reconciling the z34's very round, bulbous tailend with the sharper, angled silhouette
Nissan is going to really tighten up the rear end for it to flow correctly if they want sharper edges. Look at how the F-Type does it:
The rear seems to be shorter than the Z34, much less over hang. Also, the slope of the rear hatch does not curve back up like the Z34 - it just comes to a more abrupt, defined end. The rear fender arch flows into it flawlessly, and the bumper follows those lines as well.
The Z34 rear hump where the tailllights are located is probably the biggest flaw in the design, that whole area is just too much mass. I suspect they had to do it for cargo space, and also because the platform would be shared with the larger G37 coupe/sedan
Fortunately, the official silhouette released by Nissan seems to do a much better job than these renders:
Look at the rear hatch and the line is creates. That line (c-pillar) flows continuously to the very end of the car. It doesn't curve out and up like the 350 or 370z; it keeps flowing downward and then ends sharply. This angle shows the rear fender and c-pillar better:
Looks WAY more F-type than Z33/34 - a much shorter overhang, less rear mass in the rear arches. These are all good things, and hopefully the "Z34.5" will retain the same cavernous rear wheel wells that fit massive wheels easily.
Really, the Z34's suspension is pretty good for this level of sports car. The biggest improvements will always be weight and adjustability. There's no reason why Nissan can't build in some sort of camber/caster/toe adjustment at both ends. Using aluminum arms would also help. Lighter parts + adjustable alignment are two easy fixes for the platform's biggest weaknesses