I'm a collector (not a dealer). So, IMO the only reason to "keep" a collectible (and I own many) is NOT whether you think it will rise in value or not but simply whether you still "like" it or not.
The 0770 will never rise in value like the 0777 already has because it is not "rare" and is not in high demand because of its rarity. However, the 0770 is a fine knife. I have one just like yours which I like and plan to keep regardless of its valuation. When I do not "like" it anymore that will be the time that I'll sell it for whatever price it is going for at that time.
BTW, I actually prefer carrying the Kershaw Natrix because it is so cheap, yet so similar to the 0770, but that's another matter.
In any event, if you like your recently rediscovered 0770 keep it. If not, sell it and pocket the profit that you can make on it now. Keeping a knife that you do not like on the chance that it may rise in value so that you can make more on it later is pure speculation. You could make more later or you could make less than you could make by selling it now. There's no way to know which will happen later.
As they say, "a bird in the hand is worth 2 in the bush."