Another tidbit I picked up from a wise old detailer back when I was in the business: ArmorAll (or anything similar that doesn't contain a sunscreen) can actually act as a magnifying glass for UV rays. When applying an oily substance to any surface, you're actually adding a thin layer that can multiply heat absorbsion and you end up simmering the top of your dash in hot oil. You can see this affect by swimming around in a pool on a sunny day - the sunburn can be twice as bad, and occur twice as fast - under the right conditions, the water will magnify the sun's rays. Coating plastics in an oily film carries the same principal.
Something I learned from seeing some pretty bad examples of neglect: The headrests and tops of the back seat take a real beating from the sun - use a leather treatment that has a UV blocker, and you may even go as far as my mother did on her Accord after some damage had already been done - placing some sort of cover over the top of the back seat. The leather on the tops of her headrests was COOKED after a couple of years of neglect, and non-tinted windows. I applied some leather treatment to stop the damage and she threw a small blanket in the back window shelf to prevent further "sunburn". If you have your windows tinted with a product that actually blocks a good portion of UV (some 'smoke' tints actually don't block much UV) then you don't have to be as concerned. If you have NO window tint, pay close attention to this area under the rear window (sedan).
