One thing I really like in the Tome of Knowledge is tracking which set pieces you have found. If you are going to have a dozen sets of armor for each class, in assorted tiers, track them. Three reasons, the last of which is where I am going with all this:
- Checklist. As a developer, this gives your player a menu of “what do you want to do next?” As a player, this reminds you of what you have in the vault. This is less necessary in the sort of game that has clear tiers where you work on one tier at a time.
- Achievement. If you need to pitch that old armor to make room for the new, it would be nice to have some sort of trophy, like an achievement tick saying that you had it. Do this for each piece, not just for the full set.
- Cosmetics. Combine it with an appearance system so that you can display any old set (possible restrict this to full sets, rather than single pieces). Completing a full set effectively gives you a new costume. Maybe I want to show off, or maybe I really liked the look we had three or four tiers ago.