We went about two years ago and found jayco there. Not as big as the June show but big enough.
Last time we went it was free but notice they are charging now so they must be offering more!
I'd definately advise going ...the only risk is that they might not have the van you want on display but I'd be surprised if that happens but you won't know if you don't go....or ring them first.
One big advantage is that it's easier to compare models and makers if they're all in the one place...as long as you do that before total confusion sets in.
We have friends who intend going for each of the three days and will only stop when they have made a decision and bought.
Good luck