I too have just joined BIBOA (posted the application this morning).
I am about to take delivery of my brand new Avon 6.2 with Honda 130, but intend keeping my Narwhal 4 Metre with Suzuki 40 for use when I'm aone, or when a smaller boat is more practical.
I would support the organisation of trips through BIBOA rather than a separate organisation.
As for impromptu trips as mentioned above - does BIBOA have a club pennant that can be flown to identify members to each other? - would seem to make sense rather than having to ask everyone you see if they are members.