Ok, so what is the consensus here about buying these UV protection sprays and using them on the dash and inner sides of the doors? Is it necessary and if so what product is best?

I have a 99 car and never treated the plastics and they appear fine and no fading or chipping.

Thoughts?

 

UV is particularly damaging to plastics by attacking the chain bonds. That's why safety helmets never should be left in sunlight. paint and additives can resist UV damage but aren't absolute protection.
Indeed, the sprays and coatings like armorall, the oldest I think, are protecting the plastic from losing the additives by evaporation from the heat to resist cracking from the plastic polymer chains and hence your dashboards.. take a good look at dashboards on cars in junkyards to see the range of damages and whose dashboards are the most vulnerable.
as for your 99, just how much is your 99 exposed to sunlight? if you lived in AZ your dash might not have survived so well.

 

I use Meguiars quick wax / X-press wax for this. You can get a gallon on Amazon for 30 bucks.