Heres my personal take on it: If you 're going for navigation use as your primary reason to buy StreetDeck OR Centrafuse, I'd have to say this: "Go with neither."
StreetDeck uses Microsoft MapPoint as its software of choice.. Not a bad choice, but not as good as others. I haven't personally used it myself, but from what I've read, it's decent.
Centrafuse uses Destinator as it's mapping source (I think because of cost??). Not a good mapping program by ANY means. I actually bought Centrafuse with all the navigation options and ended up getting rid of destinator and buying iGuidance 3.0 instead.
Now, if it were my money: I would use RoadRunner as it is currently the most customizable frontend out there, totally upgradeable with new features coming out daily (don't have to wait for company to release a new update..) and on top of that, you have free reign of mapping programs.
I chose iGuidance myself, like stated above because it seemed the most logical of choices when purchasing navigation software. I LOVE iGuidance. I know there is flaws in the software, but it still rocks either way. I love the different skins I can choose with RR and all the different options there are.
As for you saying the HARDWARE is pretty straight forward, I'd have to argue that point. Hardware is the biggest pain, as there are WAY too many options out there. You throw on Road Runner as your frontend, and half the job is already done. You'll then just have to figure out which skin you'll use, which navigation software you're going to use (iGuidance all the way) and any external apps you'll want to install..
If I'm totally wrong with this thinking, anyone, please correct me. It IS almost 1:00am (I have 3 kids) and I'm exhausted!