For me it was after I looked at what I could buy with my "corvette budget" the ZR-1 was the most bang for my buck. It turned out that my 90 fit nicely within that budget, so that's what I bought.
I guess I could have waited till now and got more ZR-1 for my cash, but then I'd have missed all the fun that I've had for the last 4 yrs using my 90Z. Yep, I like my 90 ZR-1 just fine!