I think the dealmaker for a 135 or 120 scanner going forward is not IQ, but rather the ability to scan a whole uncut roll of film automatically. It doesn't seem like this would be too difficult to implement.
IQ for Plustek's 7600-series products seems pretty good, comparable to Nikon for 1/5th the price. My impression is that for marginally better scans, the cost factor goes WAY up to Imacon levels. I'd say that, for those few frames that you want to print big, it makes more sense to send it out for best quality scans. This might be a dozen frames a year.