Just thinking aloud here, I realise there may be a huge problem with this idea that I just haven't thought of, but...
There is one way you could solve it without nerfing the sets OR having the sets skew duelling the way Vic mentions if they fix duelling to be meaningful...by introducing a new, long, tough, fierce quest (in the way that was suggested here and there when the sets were first released) with reward items that are broadly equivalent to the sets. That way the non-nugget users could eventually restore enough of a balance to keep interest, even if it took them a good while, without the set owners feeling they had wasted their r/l cash?