1.  You're comparing an old, small GPS with a new, large GPS.  My phone is larger than those old tiny GPSs too, but my GPS is WAY bigger than my Galaxy S7.
2.  I don't, my GPS is normally plugged into my lighter.  
 
3.  My GPS tells me and shows me, I have much better visual skills than I do listening comprehension skills, I can just glance up and tell without having to pay much attention to it.
5.  Sometimes you miss the signs if you're looking for other things.
6.  I hate sound coming out of my phone period.  Don't care if it's phone or whatever.  I don't want to open up some stupid website with embedded video that auto starts and have it blaring.  It's annoying.
7.  I rarely talk on the phone, mostly I interact via text or email and voice to text is a big piece of crap.  It was better on my Windows phone, but then most things were.
8.  Definitely agree on the traffic updates, it's why I still use google maps at times, but usually in conjunction with my GPS. 
Mostly though, it's what I'm used to (as I'm sure is the case for you).  I keep my GPS at the top of my windshield right next to my rearview mirror.  It's second nature to me that I can glance up and know how fast I'm going, what the speed limit is, how far it is until my next turn, and where I need to be.  I usually look at it at the same time I check my mirrors, which is often when driving.  
BTW, most new GPSs have a more accurate speed reading than most vehicles' speedometer.  Mine varies significantly.  My Mini is a good 5 miles off at 70, the Juke is 2-3 off, my S2000 hits it pretty close.  I like to keep my cruise control at exactly 5 over so my GPS takes the guesswork out of that.
There are reasons that a body stays in motion
At the moment only demons come to mind