investment at LHR, unlike in most cases, is constant.
Again this is mistaken. Investment at LHR ground to a halt pre T5. Money was spent on shops and the airport itself went to Hell in a handcart. T4 opened in 1984, after this BAA focussed on building Norman Foster's new airport, London's third at Stansted. The plan was for legacy carriers to move in and free up space at LHR. Indeed Air Canada had to go to court in the late 70s to prevent BAA kicking them out of LHR to STN !
Now the airlines told BAA they were not interested in paying more at LHR to subsidise a facility they had not asked for in Essex. BAA screwed them over anyway, STN was built, Air UK moved in and that was pretty much it until BAA gave it to Ryanair for next to nothing. As soon as that happened, the legacy market which had not really wanted to move, and having sampled STN in the form of SAS and LH moved right back to LHR and LGW. The STN market that came about was a new one driven by FR and EZY using a terminal that was far from Low Cost and was paid for by carriers at LHR and LGW. Now STN may now be profitable but don't go rewriting history and portraying a plucky little fighter up against the big guys as that's not what happened.
Whether the market wants a bigger STN we shall have to wait and see.
In order for BAA to want such dramatic price increases at LHR now STN is being sold off really does say a lot about what STN really did for them!
They're hiking prices because they can, and because they're no longer a group which can spread investment across the group over time. It's LHR now, that's rightly the focus. They've only had decent facilities again since 2008, T5 was a generational change allowing the redevelopment of the rest of the airfield, T2 is coming. Next to Crossrail this is one of the biggest construction sites in the UK. If you think profits from Ryanair at STN can pay for all of this, then I have to say I think you are quite wrong.
I like STN as an airport and I used to use it a lot when FR flew to where I wanted to go (!) I wish MAG well in making a return on their investment.
intentions to operate it as a fast growing, friendly, low-cost alternative gateway to London!!!
Except that this is exactly what they ended up doing with a based fleet of Ryanair, easyJet and lots of inbound Air Berlin, German Wings, Norwegian et al. I am sure MAG will aim to repeat that feat.