The Z cars were and still are great cars. I had a 72Z. The biggest bugaboo is rust. Especially above the front wheel wells. This is a unibody car and the metal was especially thin. The "box" frame of the unibody extended up into the wheel well and easily rusts out. The cost of repair is much more than the car is worth. On the plus side, parts are fairly cheap and readily available. Victoria British carries most of them. I use them of my british cars and they have great parts catalogs. You can find them here:
http://www.victoriabritish.com