Thanks for the input!
I guess one way to fix the shop issue would be to have shops have two categories of items: "vanilla" which are every item of every category of things the shop is selling from the appropriate tier range, and "special deals" which are randomly generated items with random special effects. (Right now every item is fully defined by its tier and category, I think it'd be fun if items could have random affixes and stat changes to make them a bit more unique). If you want a good sword you know you can find the highest-tier one from the store's ordinary selection, but if you're lucky it might have a special one in right now that has some unique flavor.
Disgaea had pretty in-depth item mechanics, and one of my biggest regrets with Shattered World is that I didn't have time to copy those as well... for the remake I'd definitely get some system in to have more item variety (maybe even a system that lets you upgrade items so they don't get obsolete once you get access to higher tiers, so you can bring along that Lv.1 sword with an awesome ability through the entire game if you want to)
Another idea could be to have some sort of crafting system that lets you make any item you want using the same materials... then you would have even more control over what items you get. I can see how I could make this work with the "more personal items" thing technically, too... items could provide skills the same way as Essences do, and you'd craft equipment using Essence and some special crafting materials... they could all use the same system, and every effect I could think of could be implemented as a passive or active skill. Maybe the reverse could also be a thing, dismantling an item to get crafting materials and the Essence of any skills it provides when equipped, so you can learn them permanently or put them into new items with higher power?
Speaking of RNG, by the way, you're guaranteed to get an item drop every 10 items and a rare item drop (an item of higher tier than the battle rank) every 100 items. I figured it was a more fair way to distribute loot than having 10% / 100% chances since it's fair both in the short and long run, and since battles against 10 enemies at once or more isn't uncommon you don't need to sit through too many battles to get those drops (every enemy you defeat adds 1 item to the battle loot table).