I am not saying necessarily otherwise. But Waves wouldn't be the first big company to charge for less than "noticeable"...
That's not the point though, there are many other factors that will make the sound in a live venue loose it's premium processing. In the moment the signal leaves enters the cable, to the mixer, to the amp, to the speakers, everything can and probably will make the difference between regular effects and Waves MAXX less dramatic.
Of course, when you talking about the studio closed system, the differences will be heard, but "If you were listening to both of them running through a PA at a typical gig" - as the question was, I think maybe 3% of the people will tell the difference. (Totally unscientific determination! ;))
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Yamaha S770, Studio One 3, EMU 0404USB, ESI, ATH, Dell. And others.