I think in most gig situations large enough to warrant using a wireless, you would not be able to notice too much difference in tone. I have had el cheapo wireless before now, but a £20 cable normally suffices for most situations. If I was playing arena stages every weekend, I would use wireless all the time. But as it stands I have done probably 3 gigs the last year which a wireless system would have been nice.
And, I find that the smaller the stage area, particularly the miniscule corner assigned to me and my equipment, the more I need the wireless, because the cables just get tangled up in my feet otherwise. The last thing I need is to stumble on the cable and take out my rig and guitars.
While dancing around from stomp button to stomp button, and manoeuvring around volume and wah pedals, the last thing I need under foot is a cable.....
(personal opinion, of course....)
Not to many bands mixing themselves in the clubs here...If you are like most gigging musicians, you are doing your own mixing and this is of INFINITE value.