The 370Z ain't exactly cheap-to-keep, but it's not too bad. IMNSHO, no worse than most other cars from the last 10 years or so. There have been some oil consumption problems; usually occur/fixed under warranty. The Steering Lock Unit is a common problem that is expensive to fix out of warranty (~$1000-1300), but is easy to prevent. Quite a few people have had a problem with the rear hatch opening properly, but, even if out of warranty, it's not a biggie ($45 or so for replacement hatch springs that are very easy to DIY).
Read through this site, other 370Z sites, and the
NTSHA site for more info.
But the 370Z is only four years old, so who knows what tomorrow may bring?
I'm been very pleased with my 2009 - I'd buy another. Can't say the same about my local dealer, but I've found another that seems to be much better.