I wouldn't say 32 GTR prices are dropping... now that they are becoming a collectors item, and with the 35 GTR out, everyone wants a GTR again!
32 GTR's are awesome. Don't get anything under 19k here or in Japan - I've seen some 10k GTR's going on a few import websites and they look very suspect...
It also depends if you want a stock or worked version. There's many, many thrashed examples coming out of Japan that have been drifted and driven into the ground with very poor mantinence. Watch out for the GTR's with accident damage, too. And make sure to check for rust, as some GTR's from certain parts of Japan have rust spots in the guards, boot, etc due to the damp and salty conditions that the cars subjected to.
And never trust the k's on the speedo. They're more than likely wound back (easiest way to tell the mileage of a GTR is to check the steering wheel condition, handbrake and gear shift boot and especially the pedals), so always get the 100,000k service done the minute you buy it.
But overall, if you get a nice, clean, well-maintained example, they're well worth it. They're alot of fun to drive and are a real head turner. And of course, they won't lose their value anytime soon.
Best thing I've ever done is to buy my GTR!