Not sure why people are so concerned about people exp'ing with lower level gear - I think the chances that "low grade" gear are going to have worthwhile inheritable stats to high-level players are roughly zero. If somehow this ends up being the case, I think it's a gear design problem and not a Materia system problem.

Also, I think it's safe to say that it'll take multiple gear repairs' worth of effort to accumulate enough Attachment Points to create a Materia. To ensure this is a boon to crafters, gear repaired by actual players should receive an Attachment Bonus. This bonus should not vary with HQ repairs or anything like that.

I'd personally love it if they removed gear's stat penalties for being damaged, and just made is so that it significantly slows or even eliminates the rate at which you accrue Attachment Points. This basically flips the durability system psychology around so that keeping your stuff repaired is something you want to do because it'll help with future goals. It's also beneficial to the player without being detrimental to the group.

...In fact, I'm going to go suggest that now.