Before I put a Cliffy on any game, I try to find another example with more plays than mine. Some games need Cliffy's, some don't. SOL hole on a factory AFM? Definitely needs a Cliffy. Slot machine scoop on TZ? Surprisingly often, nope. A great place to scout potential wear is the PHOF. They don't use any protectors that I've ever seen.
Another consideration with Cliffy's is that they always make the shot slightly harder. Most don't notice it, but they do. If you're already struggling with the shot, a protector will not make it any easier. As mentioned, if you decide to install one, clean the area and take a pic first.
Collectability and resale value should not be considered IMO. Just ask yourself two questions. Does in need it and how will it play with it installed.