I drove a 4 banger before the Z (atlima sedan). Since I still have the option of driving my altima, I dont feel the space being restricted in my Z. Rarerly do I use the Z to lug around luggage and etc. If I have too it still has some space in the back for me to put some things in.
Might I suggest a g37 coupe? Still sporty and has 2 extra seats. Just a thought but im all for a Z, heck I own one, good luck on your decisions.