Well, what you're saying about the limited impact of 'normal' light on print degradation seems at odds with what Mark is indicating, Alan.
The coatings/varnishes used on paintings are very different from the sprays used today such as the Moab/Hahnemuhle/Premier/Epson. Those varnishes are more like the roll on coatings used on canvases today. They'd be similar to a spray on varnish that actually provides an overcoat protectant. The inkjet print sprays noted above don't do that. They absorb into the media and provide, as near as I can tell, basically zero protection to the surface and the ink. When I spray one of those on a canvas it provides basically zero protection against scratching or other abrasion damage. It does zero to protect the edges from cracking when stretched. I've tried, just for kicks, spraying a couple paper prints just as an experiment and they do nothing on matte paper. On glossy stock, it's a bit different. The sprays seem to, for the most part, sit on top of the coating already on the paper which might provide some additional protection but the look isn't great and if a very high degree of care isn't taken, the spray will pool and puddle on the surface.