You can spot until your heart's content round the back of the runway. I'm not sure that a 'Spotters area' is high on MAG's or any UK airports agenda as I can't see it pulling in any revenue from the spotters with their packed lunches.
I wonder if it makes money at Manchester? Parking at £3 hour brings in revenue and despite some people bringing packed lunches, the cafe seems to do good trade. However it is close to a big city, unlike Stansted, and has a certain pointy-nosed attraction in a hangar with restaurant popular for wedding receptions etc. And A380 passes twice a day. I think it does bring in a lot of goodwill to the airport.
Not sure who pays for exhibit maintenance though.