As a business traveller I fly to where I need to go. If the airport is part of an integrated transport system so much the better. However I don't consider it when I book, if it's somewhere I need to visit then I just have to go.
Slightly different if going on holiday though, if I can catch a train or tram virtually to my hotel/apartment then it's a plus point.
So I do agree that a dedicated train/tram station would be good and would encourage people to use public transport to and from EMA. My guess is that the areas such a service connects to would probably benefit from extra visitors who have passed through EMA.
But would it make a major difference to passeger numbers at the airport? Maybe a little but nothing spectacular is my guess.