Here's my take on this...
In September 2012, I was working a contract gig for Comcast. I had just completed a train-the-trainer in St. Paul, MN and my assignment placed me in Portland, OR for the next 2 months. When calculating my travel expenses to Oregon, on top of the fact that I've never visited the Pacific Northwest, I decided to drive from St. Paul to Portland. I had a Lumia 900 at the time and I used Nokia Maps (what it was called before changing to HERE! Maps) to get me from A to B. From what I remember from my Android device and Google Maps, you can get it to download your itinerary and cache it, but that doesn't really help when you decide to alter your course after the fact as I learned while traveling through West Virginia, where cellular signals can really get lost.
Anyways, I plotted my course to Portland, but after I began my journey, decided I wanted to hit a casino, Mt. Rushmore, Yellowstone, and a few other places. Nokia's maps can be used 100% offline and driving through some of those remote areas and mountains was a dream! I lost data several times through Montana and Wyoming and South Dakota early on, but my navigation kept up thanks to gps and having all of my maps already downloaded. It was very refreshing not to have to 'guess' if I was going the correct way because my mapping application couldn't get my current course due to lack of cellular signal, which I can tell you first hand, was lost for miles at times (and when I say miles, I mean like 30 minutes or more).
I'm not totally knocking Google Maps as I think it's still one of the better navigational systems, but I would take my HERE! maps any day on road trips, and I'm a HUGE fan of driving vs. flying. If you haven't made the plunge yet, I think you may be pleasantly surprised.