It's funny, great minds run in the same channels. Doug and Robert.
As Doug said, i had a 1999 Miata and learned as much about it as I could. i did some changes to it like adjusting camber front and back, Koni shocks, bigger stab bars, etc. I NEVER had any problems with the back sliding out, it was perfectly neutral in hard cornering, just ask Fudgie

I had a knowledgeable guy do the suspension and he said that the Miata had FULL adjustments for camber, castor, etc, on both front and back, with full upper and lower suspension arms. Some think that the Miata is strut suspension, it is not. The same guy said that full adjustments were not available on the BMW Z3.
Doug, I talked to my friend who has two Z3's. He actually drove the Z3 at New Haven and has told me to steer clear. 91k miles and no maintenance. The plastic radiator, plastic water pump, have not been replaced (should have been a long time ago) and he said it doesn't drive like a Z3 should. Fluids weren't touched either. It was totally maintenance neglected but looks great, a real fooler! He estimated about $4k in repairs and maintenance to bring it up to speed.
I might consider a Z3 but not that one. i prefer the Miata even though it has modest horsepower. The American feeling is that if it doesn't go, put in a V8 and that would change the handling of this well balanced car. I'll take a Miata over the BMW anytime. The sweet sound of that four reminded me of the same mechanical perfection in the Valkyrie's boxer six.