my personal take: if you need to take more then 2 people or a lot of cargo, then take someone elses car or a cab or rent a Zipcar (they have them in DC I think). And roadtrips: The Z was designed for GT (Grand Touring). As in, long distance travel in great speed and great comfort for 2 people.
When I get my Z, it will be my only car, just like my current 300ZX Turbo is. I have not missed the back seats, though I was afraid at first. Im young, Im single, I have a ok amount of money, Im going to have some fun.