I personally interpret the 'boys with toys' comment to be an ill-founded and patronising attempt to discredit the opinions of myself and hundreds of thousands of other people rather than a difference of opinion.
I took it as an attempt to discredit the business plans of airports, not a slight on the people of Sheffield (or Coventry for that matter).
There is absolutely nothing at all wrong with wanting to see your local airport (or football club or city centre or anything else) doing well, or indeed existing in the first place.
I say that as someone who spent a great deal of time supporting CVT at the public inquiry, even though they were a commercial organisation, then part of TUI. I simply believed that local people had a right to use our airport, and that the narrow minded attitudes (and in some cases outright lies) of local people needed to be taken head on.
Like a good university (or two), an airport is a good thing for a major city to have, and it all adds up in the urban top trumps game.
However, none of this alters my view that the business case to bring back SZD is there. I wish you luck with your campaign, but I really don't see it happening, for all the reasons already mentioned.
As for land value, airports with only a handful of scheduled flights are not particularly good utilisers of land. Whereas a railway needs to be continually extended to serve more cities, SZD, whilst compact, has never even handled more than 100k pax in a year, and thus a business park may well be the best use for the site, however mundane that might be.
In the longer run, even though Meadowhall is a bit of a Ryanstation compared to the city centre, if that is where the HS2 station is going, then that makes the SZD land more useful as a business park (and not as some form of fantasy integrated hub, which would need an airport 100x bigger than SZD in its busiest year). Note - HS2 is likely to pass very near to, but not through EMA.