The new Z4 has more resemblance to a Fiat 124 than the Stinger. And even that resemblance I think is more down to the fact that they're both roadster convertibles. The Stinger's design isn't copied, and no one has copied the Stinger's design. Seriously, anyone who's seeing a resemblance between the faces of these two cars isn't paying enough attention to car design.
BMW's finally gone and moved the needle off of "design-by-photocopier". This is definitely the first BMW in recent history that doesn't look like a photocopy of at least one other BMW (with the exception of the i-series cars). It deserves credit for that. If there's any BMW to feature unfamiliar styling though, it'd have been the Z car.