"There can't be many public capital engineering
projects in that league?"
I can think of one down in Holyrood which was almost as expensive, and a lot less useful.
I accept the whole of Scotland argument, joining the lines seems like a good idea. But the majority of pax flying to/from EDI must still want to get to the centre or the outskirts of Edinburgh. The airport express and local buses provide this option. Last time I flew to EDI, I took the bus which goes down CERT (#22?) to Leith. Think I was about the only person on it until it got to Edinburgh Park.
How many does that leave who will benefit, including those non-air pax who can transfer there - but presumably at a hefty premium?
I think it is a great project, but I just can't see it justifying such a hefty price tag - we are just talking about a station here, not a whole airport after all!