Re: How much of an advantage is night vision?
I got a PVS-14 earlier this year, unfortunately I still haven't shot with it for lack of a night time range. However I have spent a good amount of time playing around with it...
I think I might know what your buddy is going on about with NV being a joke. When I first got my PVS I was in Atlanta GA at the time, and their was so much ambient light that night vision offered nearly no advantage. Anyone with decent vision could see just fine at 2:00am (but I'm from the country so I hate cities and light pollution, it all seems bright to me). If he is operating in a city, I can see why he would say NV is a joke, as the ambient light is usually so overwhelming NV doesn't help much at all.
When I got back to Vermont with my PVS everything changed. I've been out kayaking on the lake with it on a clear starry night and I could distinguish shapes up to a mile away; additionally I could see perfect detail into the trees on the shoreline. Aside from everything being monochromatic you can see very well, it's really amazing technology. I was on the beach after some people had a campfire; with the naked eye it was just a black lump of coals, but with the NV it was glowing bright. Even the smallest light source is distracting with how sensitive the Gen3+ stuff is. I have also driven around the back roads with it. Personally I don't think the monocular/lack of depth of field makes a huge difference; if you're an experience driver you should be able to judge distance from the scale of objects as you drive (I was also driving roads I know well and I knew were my braking points were). That being said, I would recommend disconnecting your brake lights, because when I go to slow down it's almost blinding and lights up the whole interior...wait, don't take my advice I'm probably recommending something "illegal"... The same problem happen when I accelerate, even the little traction control light on my dash is blinding (I would turn off my T/C but it's a Mercedes and they make it impossible).
The short answer to your question is, yes. You can easily drive and safely navigate at night with good NV.
The problem with NV is that it's stupid expensive for anything useful, and like all electronics it's depreciation rate is just depressing. At the same time once you buy it, you'll never want to get rid of it except to upgrade. It's awesome, end of story.
My only disappointment has been finding a decent IR light-source. I bought a Surefire M962 with an IR filter and it's not good for much more than 15 yards with the 120 lumen bulb. On the other hand, the IR target designator on my Insight LAM rocks.