Look at it this way, aside from the rare Sears exclusives, anything else was oretty much made in the tens of thousands, if not hundred of thousands of specimens, of which at least a decent enough fraction is still available to keep the collector community, not counting the 1990's vehicles w/ drivers of course, that stuff is becoming more hard to find. So original stickers or replacement stickers, the depreciation of the loose vehicles is insignificant next to the Power of the vehicles that were never assembled, never had their stickers applied on, or that are still sealed in their packages, etc.
So enjoy your loose vehicles, and I say forget about what others might think they're worth or not! Cobra Stickers is definitely the way to go.