If you mean a knife that is worth money, it will be pretty hard to tell. Probably not production knives, I guess. And, in general, I don't really think a knife can turn out to be a good investment in terms of money, altho some might be for sure. Either way, I'm not the best one here for such evaluation.
But, remember, a knife can be worth alot more for its story.
To me, a good production knife that you have carried and used alot will be worth more to your grandkids than any "sterile" like-new knife, no matter if it's a custom.
You said you remember your grandfather carrying a Case. That knife, even in perfect condition, would be probably worth very little now, in terms of money. But, if you had it in your hands now, after seeing it in your grandpa's hands for 20 years, it would surely mean alot to you, and be worth alot.
