I just dont understand how one would expect the airport to expand and for "work to stop". There will always be improvements to be made especially at an airport whos pax numbers have grown as much as LTN in such a confined space. These are the first owners actually putting some effort in. As has been mentioned Luton isnt trying to be Dubai Airport or the newest wonder of the world. It is serving its purpose and looks like it will continue to grow and grow.
It is an easily avoided airport because most flights are still offered from other "London" airports if you really despise LTN yet the numbers continue to soar. I guess most people just want an affordable flight and can put up with an hour or so in the tin shack to get on a plane. This is rather tedious though so I digress.