That's the key, I think. At least for me. I'm not a dealer. But I found myself rebagging some bronze yesterday and I stopped and stared for a while at my copy of Marvel Feature #4. It's maybe VF at best, but I could remember where I bought it and when, who from, why I wanted it and how hard it was to find a decent copy, etc. etc. And it triggered the same feeling of 'at last I have found you' euphoria that I got when I pulled it out of the bin at a store in San Francisco in the 90's.
If the books never lose their appeal it doesn't matter what they are. The value is something much more dare I say spiritual than just their investment potential. And so you have to measure maybe how many "wins" the book supplies you, I think. Money? Check. Excitement? Check. Cultural value? Check. Personal victory? Check. Commoditizing collectibles has the very real danger of being soulless otherwise.
Silver age Marvel keys, Gold mega keys, bronze nothing in mid-grade--it doesn't matter as long as there is fire in the acquisition and retention of said collectible.