If you are going to re-dye the pad, I'd wait until after, since you need to clean it before you dye it. But I guess my question before you dye it is how dry is it? If it really is very dried out, then it may crack during the dying process.
As far as preservation of car vinyl, interior or exterior, it seems like the verdict is still out as to the best product. What you need to promote is the breathability of the pad, so don't use one of the oily (shiny) products. One of the 303 products might work the best. They promote breathability and give UV protection.