I think it's a great car for a collector, but not for someone looking for pure fun.
No experience in a regular Z8, but a little in an Alpina Z several years ago.
I would pass on the Alpina. I love the wheels, but it's a different (weaker) motor with an automatic.
The regular Z8 have the M5's V8 @ 400, all with 6MT.
The car looks ****ing fantastic; it did when it came out, and it does today. Cool shape and cool lights (even the side blinkers).
It is not eye-popping. It looks good to the trained eye, but I am not sure they get a as much attention as a comparably priced F-car or P-Car.
Cool seating position. Fun car, great for touring. Perfect to take out on a nice day every once in a while to get the parts moving. The soft top is garbage. The frame issue sucks. It doesn't perform nearly as well as other $120K cars today, but that's not the point. Never seen a white one, but black should be easy enough. Red and cream interiors were hot. Centered gauge cluster was goofy. Not sure how many Z8s they made, but I believe more than they originally announced which is why they ran the limited edition Alpina cars at the end. Not sure if these have any extra value these days, but Beverly Hills BMW had a notorious window sticker for one, $152K msrp + $152K market adjustment.
At this age, they've made it to collector car status and will continue to hold value. Nobody is buying them to rack up the miles. There's been no direct replacement, and like the CGT, anything coming down the line remotely comparable won't impact prices like a true successor.

She had a sensational sound. Daylight and yours truly.