Hi AZ,
Yes, I think a little "contraction" is inevitable everywhere as older collectors die off and the number of newcomers fails to match the same numbers. At least in the US, there is expansion in other areas. As you've said, Union is getting slightly lesser in numbers but maybe due in part to the increases elsewhere.
Here the story couldn't be more different. The NVCF is the ONLY major fair / show annually in the UK that is dedicated to this specialist area of interest. If the talking machine element is disappearing (and it most certainly is), it is not being represented anywhere else either. Mainstream antique dealers and auctions don't have any interest in these items. Rarely will you find an item described with more than two words. No effort is made to find out exactly what the item is and we're lucky to see a single photo online of anything coming up for sale. I recently contacted an auctioneer who listed one lot as "gramophone" with no description or photograph. He seemed a little puzzled that anyone should want to know more about the item before bidding!

Now just imagine that level of antipathy being shown towards a painting, 19th Century furniture or a piece of porcelain or silverware.
I also think eBay and the internet has a lot to answer for where the level of UK events is concerned. There is the general perception that you can buy anything all year round via
http://www.thesaleroom.com or Fleabay, so why bother to attend a tin shed in a field near Warwick, even if it isn't a particularly unpleasant tin shed!
I will not be attending this event again. That's one more regular customer for the past 24 years now deserting the fray.
As uninteresting anecdotes go, I note that even the dedicated website for this particular event has thus far been unable to provide any photos from the event since 2009! It
has become progressively poorer over the past 7 years with little signs of new items or dealers coming into the event from the talking machine side. Meanwhile the entry fee has risen by over 50%. For the same money I could sit on my own back porch, save fuel, drink quite a few beers and enjoy my existing collection a whole lot more with it!
We all still have the fond memories of 20 odd years ago to carry us through.
Regards,
Steve