A well considered post Beta, it is with certainty that more people are alive today who reacted instantly to a GPWS warning, as opposed to those who didn’t. Perhaps this in itself is sufficient justification for current BA thinking (as I understand it) on the subject.
I believe, though, this thread has evolved beyond the mere question of GPWS, to a wider approach in solving cockpit problems in general. SOP will never address, nor can it be expected to, all of the various creeks which most pilots at one point or another in their careers have found (or will find) themselves up without the means to paddle.
SOP is without question an efficient tool to instill pilots with good operating habits, the need to standardize a crucial safety issue. In some cases, however, it has forced us to over-ride the common sense approach of evaluating the why and where of things before reacting blindly to drills. As someone wisely pointed out above, if it were all so simple, Carruthers would be in charge.