I remember when the 1 series first came out there were quite a few comparisons to the 370Z not just on this forum but in the media as well.
A 370Z has better stock tires, a stiffer suspension, and a better differential stock. So, it has a harsher ride and is more of a pure "sports" car than the sporty premium coupe the 1 is. In 2010 or so, the 1er got some linear springs that were an improvement over the old progressive ones, which helped a bit, but the Z is definitely the "sports car" of the two, which makes it all the more impressive how well the 1 keeps up.
The Z is definitely a nice car, but it costs too much to add any significant power and it's a little harsh for a daily driver.