Tis a very interesting conundrum!
I'm afraid I primarily got to shows (when I can) to buy, be it from traders or under the table sales. In reality I've probably bought no more than two/three kits from UTS and a significant proportion from MFS, simply because he's often had what I'm looking for.
I have on the other hand done UTS myself and I know for a fact that on the second occasion I did better than a trader that was at the show. Why, as he had new latest releases available? Probably due to his demeanour and approach to customers. From my sources I'm aware that he was upset and you may well be right in saying he had every right to be. But I was getting rid of a lot of OOP stuff that he wouldn't have as he didn't trade in second hand. Clearly at that particular show I was lucky and had what people were looking for.
But to finally get to my point!
Every single penny of what I made went back into the hobby through traders. I didn't spend it on wine, women, or beer even, but plastic kits and sundries. It's a bit like energy in the universe, it's never lost, just changed in form. In fact Duncan did quite well out of that sales frenzy!
I like the chance to browse at what others are disposing off because of taste changes etc and if that is stopped then it may just deter me, and others from attending. Telford is different as there are so many traders and I'm there to buy!
I do like Steves idea of an area where under table stuff is actually away from the displays, partly as it'll save me time walking round all the club tables. However I'm not sure how it would be done as part of my enjoyment is sat nattering to the friends of made over the years on said displays and I probably wouldn't bother if I had to sit on a table all lonesome. So my 'dead' stash would stay with me (Don't do eBay) and not get recycled into the hobby freeing up cash for me to blow with traders.
So a slightly long winded opinion that may not be very popular, but it's what it is!