A few little cost factors you may want to consider.
The costs of having Campaign at Crystal Palace weren't all incurred by hiring the place, they were also from the massive set-up, take-down and during-the-event staffing costs. How many of you have any idea of what it takes to just get the netting up and down for a Millennium event? Or how many people it takes to get a place spotless after a tournament (all of whom want paying)? The "cow pasture" scenario doesn't have acres of surfaces that need to be cleaned, you can just let the rain wash any paint away. And you can take a couple of weeks to build the venue and take it down afterwards, not be restricted to a week or less either side 'cause they need the site for something else.
Also, Niall's organisation is based in Surrey so all his staff live around that area. To move the CC to a more northern venue would mean he would have to pay travel and hotel bills for these staff, approximately doubling his staff costs.
For those who are advocating a different sports arena for CC, you are going to get the same problems they had at Crystal Palace with the majority of them. You have a large stadium area able to accomodate 3-4 fields max (depending on the stadium & field sizes), then you have to go outside the main area for all the other fields. Then you have to find somewhere with staging for the teams - you try finding a venue with enough indoor staging for 160 teams, all within a couple of minutes walk from the fields! Car parking is another issue, as most of the non-international arenas can't park 5-600 cars nearby. If I use Ashford as an example, that was a superb tournament held in an international sports arena BUT, there were only 36 teams and I doubt that the venue could have catered for double that, let alone 4 times the number. Yes, there may be a few around (e.g. Gateshead?) that could fit the bill as well as Crystal Palace did (though probably no better), but after the comments about the distance people has to walk to some of the fields who can blame Niall for trying something different?
And no, I know very few ballers who would be happy to take full Millennium kit plus all their other stuff on a train!