Are torque wrenches worth it?

If you have a torque wrench that's only +/- 25% there is something seriously wrong with it.
Not necessarily. Let me ask you this: is there a torque wrench that can detect and incorporate the unique level of friction present between the bolt and the nut in that particular application (dependent on the materials and finishings of the bolt and nut, as well as any lubricants and gunk that might be present) in netting out the torque required just to overcome the friction? If it does, then that torque wrench, as you say, should not have such a broad margin of error.