If you like the Z3 but need a roof, then there's always the Z3 or M Coupe.
It look like 2002 will be its last model year. For 2003, they've got a radically new design coming out, and there probably won't be a non-convertible option any more.
As to the reliability of the Nissan or Mazda... I don't wish to start a flame war. Suffice to say that my old '91 Nissan 240SX lasted nine years with only scheduled maintenance and the usual things failing (i.e., rusting through the muffler, battery wearing out, etc.) and was still quite usable when I sold it. My '00 BMW Z3 Coupe has been to the shop at least ten times since I got it. My current thinking is that Japanese cars are radically more reliable than anything else out there.