Not sure about that large catchment for STN.
Where? NE London, East Anglia including Cambridge? From NE London other aiports can be accessed quite easily. Will be helped by Crossrail. They must protect Gatwick which has a really large catchment of the well heeled. LTN will have 50% more stands and has a MUCH better catchment too - Coventry and Corby to London including Bucks and Herts (well heeled). SEN novel but I suspect they have a good deal, still good for NE London and pensioners of the Essex Coast.
STN looks like the weakest link to me. If you have to consolidate it is the one to go.