RGuGIG. So the answer, like all lawyers give, is 'it depends.' Look, there is no doubt it's more hassle driving this car than a honda civic. But it's not like a countach or something painful like that.
Ride comfort- on the 12C is better than most regular cars, short of a Sclass, you'll be comfortable. Shmee has reported that the comfort level in "normal" mode is very good too.
Clearance- the 12C will scrape if you head straight on to things, but if you learn to approach at aan angle, you can get around pretty huge terrain. I imagine the lift makes things easier, but hear it's slow. Let's put it this way, I daily drive in NYC. It's not a problem. This is likely the biggest difference in usability from the 12C as the nose has a bigger front splitter and likely a touch lower. So I think the lift here is needed, and you need someone with a 675 to chime in how well it works.
(in/e)gress - No doubt, the carbon tub makes entry and exit a bit tougher than in a civic. If you're a relatively spry person, it's not a big deal or an issue. The less ambulatory you are, the tougher this may be. Best thing to do is go try getting in and out and judge for yourself.
Comfort. - If you get the electric seats, they are super comfy even on long drives. Most 675s will have bucket seats which are good for 30-90minutes depending on who you listen to. But I've driven with the electric seats for 5 hour stretches and gotten out feeling fresh. Further, the ergonomics in the cabin are 1st rate, as is the seating position great.
Fuel economy - it's amongst the best in it's segment. In the city I regularly get 18mpg and I drive it in manual mode (which seems to reduce fuel mileage by about 4-5mpg). A lot of folks that drive it in auto mode regularly report getting low to mid 20s for fuel mileage.
Media - if you need to do a lot of phone calls, this is not the car for you. Bluetooth and cabin noise are pretty bad. With the latest updates, the ipod playing finally seems to work pretty well. Radio works 'ok' and satellite radio works 'ok.' I took a 3 month road trip and it was pretty good. The NAV is ok. It's among the better NAVs that are built in, but that's a statement in relativity. It's great in a pinch and when there is no cell coverage on your phone.
Storage - So if you get the coupe, you have a good amount of storage. In the front trunk, you can fit 2 carry on bags, couple of smaller laptop bags and bit more. With the coupe you also get a rear shelf. I've done full grocery shopping of like 10 plastic bags worth that fit back there with no problem. In the spider, you don't get the shelf, but the 675 will have it.
Parking. I haven't had problems and I've gone to the grocery, costco, walmart etc. I just park in the back. Restaurants or parking garage's aren't a problem. But I think this depends on your level of uneasiness. I think having wrapped my entire car in Xpel made me way more comfortable with parking it everywhere (even on my 3month road trip , parking in all kinds of dives in the middle of nowhere).
Anyway, all that said, it's my daily driver. My only regret is I didn't get the car sooner. Good luck and let us know what you decide!