Of the Nissan tech's I know, they pretty much all hate working on the 300's. They're very hard to work on. Meaning not only will it take you a long time taking parts off to just get to the one that you want to replace... but you'll also need a lot of tools with low clearance in order to do it (again, very tight engine bay). As far as how reliable they are... mechanically they're great, but it's the seals/gaskets you'll have to worry about. It's a lot of hard work to replace a head gasket... which either means you'll have LOTs of fun or you'll pay a lot for someone else to do it. One of the 20+ year Nissan Master tech's I used to work with told me don't even consider buying one of these (Z32's)... that once they start to leak, you're better off replacing the whole engine or doing a complete rebuild. The gaskets/seals all tend to go around 100k.

Up to you though... they're a blast to drive and still one of the best looking cars IMHO. A great Grand Touring car.