For me - Absolutely the seat and the general airport experience (status benefits notwithstanding).
I frequently travel from the West Coast US to LHR and once I've had a little snifter and maybe a little TV on the Ipad, all I'm doing is sleeping until 20 minutes out. Coming back the other way the service does come into it a little more, but my expectations are calibrated with the fact that it is, at the end of the day, a meal served on public transport.

Having said all that, I also believe that for a Brit at least, the BA style of service is one of their, mostly positive, key differentiators and a selling point