I have been DDing my Nismo since May 2012 -- it's my only car, and I'm in eastern PA. Here's the skinny:
1. Bone stock, the tires suck (noisy) and the suspension is very stiff. Swap out for better rubber and put in some new shocks, sways, and springs to soften the suspension. Not only does the performance improve, which is typical for such mods, but the ride comfort changes drastically, which is very atypical for such mods. It's crazy how much more pleasant the car is to drive now.
2. I'm gonna get heat for this, but I drive this thing in winter with summer tires (which I absolutely do not recommend, btw) While the northeast has it's crappy weather, it also has an extremely efficient network of snow removal and salt distribution. Main roads are usually cleared very quickly. That all being said, if the roads are icy and you don't have winter tires, though, don't drive it that day; it's not safe and very stupid. I have missed 1-2 days of work this year because I wasn't about to risk my safety to get to work in these conditions. Snow in the northeast is unpredictable; some years we get almost no snow, others we get tons. Not worth fussing over if you like the Z. You'll find a way to work it out.
Having a second car with AWD helps (as does family close by with alternative modes of transport, like a GT-R with summer tires, a 911 with summer tires, a Mustang with summer tires... oh wait, wrong season)
3. I get 17.7 mpg all around, and I use the fun pedal without regard to mileage. Honestly don't give a hoot. I'm about to go forced induction, also. Bye bye, three digits next to the MPG!!
4. Ground clearance. After removing shipping spacers from the factory (dealer should do it before vehicle delivery but are notorious at forgetting), the car sits about 4.5" off the ground at stock height. Going up even moderately steep driveways requires a good diagonal approach, a careful right foot, and a complete disregard for the bottom (not visible) part of the front bumper. You will scrape; it doesn't bother me as long as the visible, painted parts are ok. If you lower it, speed bumps and minor highway dips/bumps at higher speeds can cause a little ground contact (with Swift springs, you're looking at about 3.25" of clearance in the front. See below.
Again, though, swapping out the suspension and adding new tires are the best things you can do to make this car far more livable as a DD. I don't regret going with the NISMO one bit, and the pure pleasure I get from driving it as well as the attention it receives makes it a killer ride to have.