As yet another with "40 years in the business" (45 years actually) I can see where they hope the business will come from and that is largely inbound European traffic.
Over the past year I have represented one such airport in discussions with both existing and start-up airlines and their enthusiasm for SEN has been a consistent feature. One European airline with firm plans for SEN sees 70% of its traffic being of inbound origin and one of the start-ups is making a similar assumption for its proposed routes.
I believe that the rapid transit times that SEN will be able to offer the traveller means it will get the nod above STN as a London arrival point, and HZ123 is rather unfair about the road system. The recently opened Progress Road improvements on the A127 have reduced delays considerably in my experience and the new link road to the A127 due to open in a couple of months will also make a difference.
Just how much influence continued high fuel prices will have I'm not sure, but a 10% to 20% saving in flight times from, say, CGN compared to using any other London airport will surely become a consideration.