Did you pay your trainer and enchanter to upgrade the runners? Better armour should help them be successful more often, and better weapons helps them return with more stuff.
I upgraded my runners but they would still keep asking for more. And you have to pay to heal them. It seemed to be a kind of a black hole. Essentially your'e paying a very high price for a few potions and enchantments in order to save the hassle of gathering materials. But I think it would have been better to just have the option to buy ingredients from merchants if you want to avoid gathering, rather than going through all that time-consuming hassle of going to your skill trainer and blacksmith to equip them, then going to your alchemist to heal them when they still come back chewed up and demanding more. The game makes you pay a pretty stiff price for the luxury of having servants go and get materials, but they could have accomplished that just by having specialty merchants charge a premium price for those materials. That whole aspect of the game seemed a little overcomplicated.
I have to say that after reading some of the responses in this thread I'm tempted to try a 3rd playthrough with a pure character build, just for the challenge. And do it on Nightmare.The replayability of this game is one of it's best features. I'm up around 275 hours now almost at the end of my 2nd playthrough but I don't think I have really come close to exhausting all the possibilities DKS offers.
