Im going to go against the grain here. I love my stock nav unit. I upgrade my Nav disc yearly (for free, burn it myself), and I have installed a bluetooth adapter.
I was also the first, and last person, to install the 2 disc 9-7x unit into my truck. So I still have a CD slot, while using the Nav Disc, although who uses CD's anymore? But this mod is not for the light of heart, and took a lot of trial and error to get it to look right.
I installed a Windows CE, and then a Android, nav unit in my Hyundai Santa Fe, and I have to say, it was nice to have all those app store options.. Until you realize its a distraction. Keep it simple, avoid the distractions.
On the downside thou, the stock NAV unit is also quite a bit more expensive. And once they start having read errors, is all down hill from there. I am going on 10 years on my 9-7x Nav Unit, and still works flawlessly.