Whilst I mirror your thoughts to a degree (as I am a staunch advocate of the 'less is more' route), there is a decline in Z32 ownership and as a result the amount of dreadful ones you see is also on the decline. I've noticed a lot less poorly modified examples around but I also notice a lot less poorly maintained ones too, the two aren't always linked
Traditionally though, the Z32 has been a real victim of the 'Max Power' and F&F scene by the billy-bolt-on and airfix brigade. It's a real shame as the car is a naturally beautiful and timeless car and things like big ungainly bodykits and lairy colours just do not work well on it AT ALL. Other cars with more aggressive lines can get away with it such as Skylines etc. But there are some modifications that really should be left for the dustbin such as undercar neon lighting, shopping lists, multi coloured wheels etc. As far as the Z goes, I completely agree with your comments regarding the rear lights. As a design piece, the stock rear lights are totally integral and tie in a lot of lines on the rear of the car and I too cringe when I see tacky/round rear lights or whatnot on the back. The main reason the Z32 looks as good as it does from the rear are the wide slitty rear lights. They set it apart from almost all other cars. Totally distinctive, an original design and nothing else looks quite like it.
Vented wings are probably my biggest pet-hate though. Awful things, they serve no purpose mechanically (there's nothing other than a wheel arch liner for them to cool) and they mess up the smooth shape of the doors and rear quarters with a mess of lines and vents. I also don't like those great big razor blade spoilers, any bodykit from Veilside and Wings West, Greddy bumpers, most vented nose panels (the ones you more commonly see).
I also agree on wheel selection. It really is a killer scenario and poorly selected wheels ruin the stance and overall appearance of the car to the point where stock wheels would have looked better. They can literally make/break it.
I think it all comes down to knowing what will work with the car rather than what you like as the two don't often go hand in hand, I like Ronal Turbos for example, but they'd look awful on a Z32 and that's fine line right there. Who am I to dictate to though, BUT, more recently general consensus points towards cars that are considered more appealing which is why things like COTM are winners in deciphering general taste. If you look at those, you'll see that most, that are monthly winners are what I'd call 'tasteful'.
So in summary, I completely agree with most of what you've said, but it seems the tides are turning and that people are either moving away from grafting half a boat onto their car, or the cars are coming fewer and farther between. I think it's a combination. As the cars become older, parts become harder to get and thus cars become harder to maintain - billy-bolt-on has moved on to pastures new.
It is cyclical, look at all the cars you see as 'retro' now. The MK2 Astra, the Nova, the MK4 Escort - cars around the same era as the Z32. They all went through the Max Power phase of hideous bodykits, stupid sound systems and awful colours, but you won't see that now. They've returned to their roots mainly. Any examples of these cars you see now are either restored items or immaculate originals. Z32 is heading that way slowly but surely (thankfully). You'll noticed though as the fads of gluing stuff to a marque/model decline, their prices go up. An immaculate MK2 Astra GTE about 10 years ago when they were slightly more common and there were plenty of butchered ugly ones were practically worthless, now they command good money. The bottom fell out of the Z32 market about 5 years ago and have been rattling along for some time. In the past 3 or 4 years, the bodykitted wonders and those held together with filler and packing tape have declined dramatically....people have noticed values starting to appreciate. I am not sure that's the case, but the recipe is there for them to start appreciating. IE, they have almost fallen out of favour with the F&F brigade, they have become increasingly rarer as many have been broken for spares and most that are left are now owned by hardcore Z enthusiasts rather than boy racers, not to mention the fact that the grey import market for them is non-existent.
They are still a car that evoke memories and a car that many people remember as being excellent. My boss who is a millionaire and owns a couple of Aston Martins absolutely loves Z32s and really likes mine. When we first starting talking about them he told me they were one of his favourite cars from the era. So it's not like a Morris Marina - a crap car that's become a classic, it's a good car that's slowly becoming a classic. Prices will go up....one day!