everything in Lockpicking and Speechcraft trees are useless, FYI
Merchant and Investor are a must for me in the Speechcraft tree.
With Merchant, I can sell anything to any merchant, without having to run from store to store to sell specific loot to specific vendors.
Plus, at higher levels you will craft expensive potions and loot expensive items, yet the merchants don't have enough money to buy the stuff. Furthermore, if you invest in the Riverwood trader, he will have 10000 gold every 24 hours. So yea, not useless at all LOL
Lockpicking, I agree, pretty useless though.