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The original idea of knife-edging back in the 70's was to reduce crankcase "windage" by sharpening the leading edge of the counterweights. Aside from the fact that you're lightening the rotating assembly, I think it's doubtful that it provides any benefit. It's pretty common knowledge that the most aerodynamic shape has a blunt leading edge and tapers to a sharp tail...not the exact opposite. Sharpening the trailing edge may actually affect windage...otherwise, it's just weight reduction. But remember, those are counterweights...if you lighten those, you must lighten the rods/pistons.
The more important thing to do is balance the assembly. If it turns out you're counterweights are heavy, it might be a good opportunity to knife-edge. Just make sure it's all balanced when done...a very small amount of metal can have an equivalent weight of several hundred pounds when being subjected to the accelerative forces found inside an engine. Making sure everything is balanced decreases bearing loads and just makes things run smoother and with more reliability.
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You are correct about sharpening the trailing edge but as it is now the leading edge of the counterweights are a flast surface. Not aerodynamic at all. Any kind of sharpening or rounding of the leading adge will produce desirable results. You are also correct about balancing the the entire assembly. If you are going this far into an engine rebuilt chances are you are getting aftermarket pistons/rods anyways so they will be light, therefore allowing the reduced weight of the counterweights.