All Vinyl's and Plastics are not created equal - most like Armor-all, some don't.
I have a 21 year old dash that I protected with Armor-all for most of the 21 years and it is shiny, soft and crack-free. It looks just like new. There are around four or five types of vinyl and plastic in the dash and around the interior of the car. Most really like the Armor-All. There is however a vinyl "button" in the dash and a plastic finishing piece around the shifter that don't seem to be compatible with Armor-All. The pieces turned milky white and are crusty and the crust sheds taking plastic away with it. These pieces were essentially ruined by the application of Armor-All.
I know this because I have a second, identical car that never received Armor-all. The dash is severely cracked and most of the other plastic is in worse shape than the first car's plastic except that button and the shifter piece which are in much better shape than the Armor-All car - not milky, not crusty at all.
It all depends on the formulation of the plastic - when Armor-All works it works really well however if the plastic is incompatible with it, Armor-All will do more harm then good.
All in all its about a 95% good, 5% harm split.
As for SPF-40 - What the heck! Give it a try and write back in 21 years and let me know how it worked.