As far as the railway station is concerned, I don't think it will make a lot of difference.
I made a few enquiries, and it transpires that, in the majority of cases, where a railway station at or adjacent to an airport which wishes to be associated with it, the airport authority has had to fully fund the station development costs and pay an abitary fee for each passenger using that station.
The vast majority of Southend's passengers will be arriving by car, not rail and that would be the case if they had twice the current throughput of passengers.
I simply cannot see the justification for a station at the airport.