I had a 2006 Z4 for many years and just upgraded to a new model (2015). The Z is a unique car, offering a look and feel that hasn't really been replicated. My 06 Z was a great little car; fast, fun, sporty. My new Z is a real step up, but retains the same sporty, fun feel of the older models.
I really don't see the comparison to a Porsche or Jaguar. These are true sports cars, meant to go really fast or to be really fancy (i.e. a Jaguar), and your paying a real premium for that. The Corvette, some say it's a good car, personally I would never own one. The brand carries the burden of being a car for the "middle age life crisis guy", not wanting to go there.
Other options, like the Nissan Z (fast and fun, but no frills) or Audi (R8 or TT, closest match I can think of, also fast and fun). Of the two, the Audi is a nice alternative and I did consider it, but for me it came down to my history with the Z.
So, my Z is not common (which I see as a positive), fun to drive, cool to look at and a joy own. It's a premium priced car, but not bad as compared to expense of a Porsche or a Jaguar or even an Audi for that matter.
Just my two cents.