The figures you have worked out are about right, but pale into insignificance compared to the the other "tourist" things going on, such as hotels, guest houses, etc etc etc., not to mention the Nokia Festival, followed by the Bestival a few weeks later, and of course the sailing side of things which attract huge revenues for the Island.
As for shopping, as most people buy in supermarkets, the income is taken by the likes of Sainsbury, Tesco, etc etc, the once local shops have al but gone, thanks to them.
We have never had a helicopter place on the Island, we do have Britten Norman, who make the Islander and Trilander aircraft.
Westalands as I think you were referring to produced aircraft parts , such as wings for various aircraft, and of course the Hovercraft, but has shut down now and the building is being taken over by a very high quality luxury yacht maker specialising in stainless steel hulled craft.
As for "a few market gardens",totally wrong I am afraid, yes we do have them, one of wich supplies most of the supermarkets with all their tomatoes, and is the biggest glasshouse in Europe at the present time.
Then there is the world renowned Garlic Farm, who supply world wide.
We also have the the largest producers of GRP products in the UK, from small mouldings to luxury yachts, motorcruisers and fishing boats, wind turbine blades, motorhome bodies
Add to that BAE (Radar) who develop new Radar technology and train operators from all over the world.
At least here on the Island we still speak English when in the company of visitors, unlike some parts of the UK who revert to local dialect.
These and many other employers actually do contribute to the Island economy as the workers, mainly local people, live here all year round.
It would be a very silly idea to rely on the 12 week season for economic stability.
Are we self obsessed, maybe, but we have seen enough of "incomers" wanting to change the way of life and values of the Island to become more like where they have come from.
As for labelling visitors, I am certain that wherever one travels to, the locals have a name for the visitor population.
Just as a point in relation to my earlier comment about erratic driving, today, two pedestrians were knocked over by a visitor in a car driving the wrong way along a one way street,,,,,yet our road signs are the same as the mainland.
Whilst they may be on holiday, it does not include a holiday from observing the rules of the road, but it seems it does, especially as the road in question not only had the normal post mounted signs, but also white letters about 2feet high painted on the road surface .
It transpired that they had been stopped by a local man and advised that they were going the wrong way, but decided to continue anyway. I hope they like the hospitality of the local constabulary,as that is where they were heading shortly after, in a special taxi with blue lights on the top.