You need to sell a shed load of product to even break even at events like this. Not a problem if you are using the event just as a product showcase, but if you need to be making rather than losing money year on year, probably better to generate sales at your home base, virtually no extra overheads for this sort of activity. Also, once you have waved goodbye to the last modellers, you don't have a three hour strike down, followed by a three hour commute back home!
Always nice to browse through a trade stand, but there will only be a finite amount of money being spent, if this is being spread around, amongst slightly less traders, then that can only be a good thing for them.