If you clean the dash first (be it simple green, windex, or a premium product), you can use armor all to seal and protect it... the problem with armor all is it's constant misuse! You don't spray and walk away, you can't leave that stuff thick on the surface like most people that swear by it do!
I've seen people overuse gliptone AND Meguire's interior products. The best results come from 1) cleaning the dash 2)sealing the surface 3)and then using another cloth to wipe that protectant off! It'll feel like new, and best off all; the greasy look/feel won't pick up any dirt floating around in the car!
I use Autech on my plastics, (it works like gang-busters) leaves NO greasy residue, and buffs off the plastic the way wax does for the outside. The color returns to like-new, and there's very little sheen to it so I don't get blinded by glare off the dash or the reflection on the glass.
Just do it right and you'll find stuff that you like!