I wouldnt buy skills every level, i usually only buy skills from npc's that i can use as companions since if ur companion can train ur skill, you can make them train u the 5 lvls, then ask them to hold ur items (trade them) and take ur gold back. its a good way to train skills u dont want to train and keep ur money. If u already got far in the game and r loaded with extra gold, then training isnt a bad idea for skills ur too lazy to train (what else is there to spend gold on if u have what u want)