[woodsman]

I can't comment on a z3 but I can on a z4 as I test drove 2 before buying a Boxster. The '03 and '06 are very nicely finished inside- maybe even nicer than a Boxster but they are definitely smaller. The '06 had neat LED tail lights, more power ( about the same as an Boxster S) and a really sweet exhaust note. They had that gorgeous, long hood and are stylish but had no spare tire and a small rear trunk (only). The Boxster handles WAY better and is truly a world class sports car, even today, in the areas of braking and handling.
The z3 never had a big following which makes them easier to get into but harder to get out of. I say drive 'em and report back!