I'm writing up a design document for a voxel based adventure game, similar to minecraft, but fixing a lot of fundamentally broken game mechanics, or at least updating those mechanics to be more suited to an adventure game.
I'm considering creating a weapon scale from 1-10, where weapons at 1 are least powerful, and weapons at 10 are most powerful. I was considering making the materials to make the weapon most common for the level 1 weapons, and 10x less common for the most powerful weapon, but if you look at minecraft, diamonds only occur in 0.1% of blocks and they still feel too common, unless you're prone to dying of course.
In keeping with the adventure focus, would it be better to have the higher tiers of weapons only come from monster drops, or from a combination of a rare monster drop and a mineable item, or are there other common game mechanics I could use to have a super powerful weapon that's also hard to get, but worth your time to get?
To state the question another way, for the time investment, should a weapon that's 10x as powerful take 10x as long to obtain, or 20x or higher? Are there any studies that show any correlation between "fun" in how long players will grind for an item and an appropriate time investment scale for obtaining equipment?