I can confirm that the seller of secrets, and all npcs are restocking on more than just hero level up. It seems you have an infinite source of stats, gold, materials, and items too choose from.
Not sure what it is. I think its passage of time in game (e.g. sheep have a timer for fleecing them). Maybe each day vendors reset? I reached her at lvl 11, and still at lvl 12 I have three sets of books.
I wonder if knowing that you could literally boost every stat to max ruins the whole min-maxing game some are playing?
