There have been some good discounts on stuff for sale there in previous years, and a few Westfield relevant stands too, but obviously most of relevance to Motorsport or track daying type owners.
It can be damned expensive though, something to consider when you estimating what you'll save!
Not sure if it's still the case, but once upon a time, it used to be the place to get kitted out with race suit, boots, gloves, helmet etc ready for the new season.
I got a cracking deal on a Race Technology Dash 2 and DL1 logger plus sensors there, a year or two before the WF factory started offering them.
Prior to that, I got a fantastic deal on a set of Jenvey throttle bodies; show price plus a little extra, because they had a tiny blemish in the powder coat. Except, I didn't actually go that year, I just rang Jenvey up asking about show deals, in my naïveté, thinking I'd go down if it was a good enough deal. And Jenvey did me the deal anyway! The carriage charge was far less than entrance tickets, let alone parking and fuel!
I would recommend doing it once though, if nothing else, just for the novelty. I've always regretted not going on a trade day, when there's more to see. Might make an effort this year, if I can get a trade ticket.