Yeah, Google brought up the cosmetic downside, but losing the effect doesn't affect performance, does it. ?
Or maybe it does, breathability wise.
The only pair of nubuck i've had i lathered in G-wax and didn't notice any difference, though waterproofnes was my priority. 
Include a little history in your walks. Pecsaetan - Ancient Derbyshire, Staffordshire and South Yorkshire - http://pecsaetan.weebly.com/