I am looking at a new pair of suede leather walking boots. Price is low due to one boot being in a shop window and so is faded and doesn't match the other boot.
My question is: would the light damage potentially affect the waterproof(ness) of the goretex?
No. If the boots have a Gore-Tex membrane, this is a PTFE film that is sandwiched between the inner lining and the upper. Light going through a glass pane is mostly harmless. For example, most of the UV light (UVB) is blocked by glass. The only issue a pair of boots left in a display might have is color fading, that's usually due to some deterioration from the rest of the UV spectrum. Fortunately, the upper should act as a protective layer, just like your skin does.
What makes waterproof membranes fail is usually mechanical. Repeated flexing, delamination, and stretching will invariably lead to tearing of the material over time.
