Im going to sound really heartless here, but its a genuine question so i might as well ask it.
Realisticly, what does BHX need the extention of the runway for?
For flights to India, PIA's B773's already operate into BHX and India is not that far on top of the BHX-ISB flight, so they shouldnt be a huge issue. Not to mention you already had flights to ATQ with no issues.
As for further afield, an exended runway isnt going to make all the airlines turn their heads and say 'ok, well come to BHX', its too close to LHR to get the likes of MH, CX, SQ, AA (LAX), SAA etc. With that in mind, who, realisticly, are these operators that have been pining for a longer runway and will come once its done.
I know it says im from MAN and you may well be rolling your eyes thinking 'its easy for him to say being a MAN supporter', but im genuinly asking this not with bias, but intregue. I just think money could be better spent elsewhere like the new tower, more stands and better pax experience.
Its not always about chasing what you 'could' get, but looking after and protecting what you already have.