1. The spell books restock but the inventory never changes. The weapon vendors/armor vendors never have anything new except maybe 1 new item. The PS4 is definitely not seeing vendors change inventory. I verify this after each level and sort by "newest" - when the newest items are the stuff I just bought coming back, there is a problem.
I am not on PS4 so you could be correct about this being a bug. But on PC original and EE, I can verify that ingredients and spellbooks restock (but sold items are never removed...guess these vendors have no other customers except the player...). The wiki states on level up and every 24 hours (which has been my experience as well). So if you are not seeing that, it's verified that your game is bugged.
2. What high end loot? I am level 17 in the game and have yet to find 1 peice of gear I would consider high end. No legendary items either that any team member could use. I have 2 mages, 1 archer and 1 figher (Jahan and Madora). I think the highest gold item I have found was a crossbow at level 12. Nothing since then.
From level 1 - 10, all my best gears are found, not crafted (even when I have someone in the party who has craft and/or blacksmith 5). I think at some point, the level of loot starts to even out, such that higher level items will always be rare and lower level items will be in abundance (and near the end of the game, you will have to have crafting to enhance your gear in order to have the "best" gear). This is different from the loot scaling of games like Diablo or TES: Oblivion (bandits in leather and fur when player character is low level, then with full set of ebony armour when the player is high level, that was a nightmare and immersion breaking...) where the loot scaling always parallel character level. At least, that would be my guess. Otherwise, the in game economy would be horribly broken and the vendors would never have enough gold to let you liquid loot once you reach a certain level (in fact, that may already be the case).