First, my rig. '07 HSE with HD. I think it literally has every option available with the exception of headrest video screens (if those were factory options).
I find the rear locker engages OFTEN. OK, maybe not when out driving a fire road but if you get into more serious rocks ... and I'm not saying Rubicon levels of rocks, but heading that direction ... the locker will be active A LOT. And yes, I've gotten myself into spots (intentionally) where even the stock rear/center lockers were not enough and I had to break out the high-lift to get off a rock. Had I had a front locker, I could likely have continued without the extra-vehicular activities.
When you're using your armor and actually sliding along that slider with a tire in the air, you'll be glad you have a locker even it it's only the rear. And let's face it, these trucks are never going to have massive clearance and articulation so you can expect to get good use out of your armor.
I agree that ARBs front and rear would be the most capable, but the costs would be substantial and for milder wheeling or snowy roads they wouldn't work as well as the stock HD's variable locking rear. Of course, in most of those situations the standard TC would likely be adequate.
You need to weigh how you'll use the truck. Fire roads and more 'expo' type use and the TC alone should be fine. Want to push it harder and play in the rocks more? Get the HD. Want to REALLY push it? Get a pair of ARBs.
It's like the Jeep guys - The Sport (i.e LR3 w/o HD) is plenty for the average wheeler. The Rubi (i.e. LR3 w/HD), with it's full manual lockers, is very capable and can really get out there. But the hard core guys will just buy a low-spec rig because they know they'll build their own gear at a higher spec (i.e LR3 w/ARBs front/rear) than what the Rubi offers so why bother paying for it only to replace it.
As for Nav...I rarely ever use it for nav. Too much of a PITA to enter destinations and it doesn't know traffic conditions, not to mention mine is still stuck in '07 and sometimes tries to route me far out of the way because it doesn't know a new road exists. It does have more fire roads than I would have expected, though just this last weekend I found it was about 1/8-1/4 mile off on it's mapping for a lot of the old logging roads I was on, so it was of limited use. The 4x4 info screen is largely entertainment. I usually turn it on when wheeling, but seldom look at it. I have not tried the off-road nav ... I just use an iPad w/MotionX instead for that and my phone with google maps for on-road nav.