Having Ribex at Cowes would not stop me going but I would prefer a mainland location.
Just Cowes adds extra costs, carrying items etc back to the car via ferry etc could be a pain.
The main thing however that would decide if I went or not, rather then to location. would the static stands. RIBS aflote are great but as I dont plan to buy a new RIB every year it would be the static stands that I would go for on a yearly basis.
The other option is would it not be possible to hold a RIB show, on the same dates as the Southampton boat show at a close by venve. That way you have all the static stands, but all the RIB's close by if thats what you ar looking for. Just a thought