I think you have researched it well. The spray in liner will do little other than protect the bed from scratches. Even with just a camper and a rubber mat, dirt works its way underneath and will scratch up the paint over time due to even slight motion. The spray in liner is much tougher at resisting the scratches. If you do not care about that (and many people do not, it is a truck after all) then I see no point in the spray in liner. In any case if it does get scratched, you can always do the spray in liner and cover the scratches, it will look as good as any spray in liner.