Value - well that is an interesting one - always hard with something unusual, with what is obviously a limited market . Condition will be critical. There is some suggestion it has 0km since rebuild but what was rebuilt, how well, and with what parts?
When sorted these cars aren't particularly temperamental in my opinion. They can suffer from overheating - using appropriate oil, modifying the dizzy to give proper vac/boost advance/retard (the original approach was to lock it) and doing everything you can heat-shielding wise to keep the turbo heat away from everything else seems to do the trick (and the dizzy mods improve driveability).
If the turbo needs rebuilding it will set you back whatever the going cost of turbo rebuilds is today (probably almost as much as a new turbo unfortunately).
The breathing is really weird because of the turbo and restrictive plumbing in front of the carbs when off-boost and then forced induction coming in. They seem (though I don't really know what the original jetting was) to have been set up to run excessively rich "everywhere" (safer on pistons that way I guess). Plan on some dyno time and some creative fiddling by an experienced carb tuner to get it right if you want it to drive well.
Oh - and anyone who really wants a drift car should (if hitting your head against the wall until the urge goes away doesn't work) go and do what the rest of the ricer's do and try to blow up a Nissan engine
. This car is *not* a sensible starting point for "bolting on" power. If you are mad enough to want a very fast turbo alfetta GTV, get the cheapest engine you can find because you will need every cent to buy/build/have fabricated pretty much everything... Don't buy this car because there are no parts on it that are useful to you.