What an experience, I am not sure that the off terminal lounge at BGI is anything special, although I am sure it beats the lounge by the gates hands down! I believe you get driven out to the steps of the aircraft and I did read somewhere that it is not just for BA First pax and that UC could use but I have only read that once.
Thinking of giving BA a go when I do Bim in 2017 (2015 will be VS, nearly there on the 300k needed) plenty of time to get those miles, as I have never flown BA long haul but will have to persuade the other half who is not a big fan of BA. Flying in First could work?
Would be a much easier choice if they did fly from Heathrow.
Did you have much interaction with the other passengers, I seem to nearly always get lucky in not just having a good crew but good passengers who like a drink/chat at the bar!