5 tire rortation
Rotation in the spare will increase the number of miles you can go on a set of tires, but it also increases the size (and therefore price) of the set from 4 to 5. You'll be paying the exact same price per mile, if you're doing a 4 tire roatation, and just replacing 4, or you're doing a 5 tire rotation and replacing 5. A five tire rotation will get you 25% more miles, but will cost 25% more. For example, you'll be dropping $800 for every 48,000 miles, or $1000 for every 60,000 miles.
I've always done a four tire rotation. When I switched to the SilentArmors, I didn't replace the spare. It would have cost another $200 to have a spare SilentArmor installed and balanced, I couldn't justify that for a tire that most likely will never be used.
The MT will look different, but if anyone ever asks, just say you have a set of matching wheels with 4 MT's at home, sitting in the garage that you swap out when you go off roading. You can afford to wear off all you tread on the highway, or that only an idiot would waste a set of MT's on the highway.
I like the aggressive look of an MT on the back.