You don't want to dull the trailing edge, but you do want to remove the wire edge that's often there and hanging to one side or the other. I always sand off the mold line on the LE but I honestly don't know if it does any good. Dulling the TE though will create more drag and hurt your performance, so don't do that.

Since you bought that hand held balancer, here's a tip for you. Held in your fingers, there is usually too much friction to see the smaller imbalances. If you will make a long "V" with cardboard or wood for it to sit into it will work a lot better.