I didn't steal much and I didn't invest in any vendor and I ended the game with 25k+ gold after paying for some expensive plot-related things (access to someone's house, and whatever other things NPCs wanted to sell me).
I didn't find any amazing items I'd like to buy like Robe of Vecna in BG2, or belts for Giant Stength, something to add spell slots, whatever. Honestly, items seemed quite underwhelming to me, most were adding bonuses that I could barely see purple being much better than blue. One spell, or advantage on rolls... Not too exciting :<
