If you get your timing correct and know the BA website inside out, BA are offering a 6 day UKL 99.99 return LHR/BWI for ABS 2007. You will either have to pay for or find free accomodation. Boat show entry is free if you have access to a RIB ( /forums/images/graemlins/smile.gif )
It's all on the web but you have to work it out for yourselves .... And Guinness is available at $1.35 a bottle otherwise it's a Pusser's Painkiller ....
IMO, the ABS is unique - It puts both Excel and Soton into a shade of their own greedy making.
The answer I am afraid is entirely dependent upon the content of each show. I perosnally think that Earls Court could be succesful if it focussed on the slightly poorer boating brigade who didn't have a £300k bonus to splash out on a new Sunseeker Mega Turbo, very long bonnet, lot's of flashy totty pad type boat. The key thing is for the show to determine its market and differentiate itself from LIBS. I don't go to LIBS because it doesn't cater for what I need, Earls Court just might?
I'm really surprised at folk wanting to travel to Earls Court a few weeks before Christmas - you tried London in December?! I used to work around there until 10 years ago, and it was a nightmare then.....