So to get back to the OP question. I feel pretty qualified to answer because when I was deciding on which car to buy I started with a long list and whittled it down to the 370Z and BRZ/FR-S as finalists. I drove both a 370Z sport package and the Nismo version, as well as the FR-S and BRZ.
I think both are great looking and performing cars and I think either one would be worth owning. In the end for me a lot of the reasons for choosing the BRZ was economics and the way I felt about the car. Just some comparisions.
Insurance - It would have been 20% more for the Nissan (YMMV) About $200 more per year for me.
Gas mileage - The 370 gets around 22mpg on a good day the BRZ gets around 29mpg with the way I drive it. If you drive 12K miles per year you will buy roughly 132 gallons more or $462 at $3.50 a gallon.
Tires - The 19's on the Nissan vs. 17's on the BRZ. I'm planning on buying race tires and autocrossing. The extra 2" means a set of race tires would cost ~ $500 more for the Nissan.
Some other things that swung me to the BRZ are the following more subjective items.
The head unit in both the Nissans I drove was exactly the same as in my daughters Versa. WTF? A $35k - 45K car with a $10 stereo.
The twins drove more like the MR-2's I've owned in the past. I loved that car so it really swayed my opinion.
You can't fit a set of 4 race tires in the Nissan. The BRZ swallows them whole.
The things that I loved about the 370Z were.
Tons of torque, more power.
I love the looks especially with the Nismo version.
The Rays wheels that come standard with the sports package and Nismo.
Good luck with which ever one you choose, but I hope you pick a BRZ
