Look, as a recent convert far be it from me to get involved in the politics, but the one bit of rugby league I ever watched regular as clockwork before Oxford RL was set up was the challenge cup final, every year for 30 years on the TV. To me, and millions of others that are/were casual viewers of one game a year the challenge cup final *means* Wembley, it's what you expect to see. Moving it back up north (which you would have to because the finances would only have a chance of working if you put everything in it) because it's "in the heartlands" is the kind of small-minded thinking that would have anybody south of the Trent saying "cheerio, don't let the door hit you on the way out."
There is an audience for big games south of the M62, the expansion clubs need to be given time to bed in, and the world cup's just been actually quite good.
I'm afraid "we need our own stadium" is probably wrong - not when the money could be better spent on development of the game full stop, rather than a totally unnecessary bauble for the big clubs you've already got. The Challenge Cup final is the once a year showcase for what RL is in England, and why people ought to watch it (having said that, I've never been so bored as watching this year's....). The Grand Final is another chance, but it doesn't have the heritage or part-of-the-furniture cut through for the non-committed Englishman outside the M62 (take it from me).
Basically, much as I hate London and spend as little time there as possible, we've got to keep the Challenge Cup final there as a statement of intent and "this is us and this is what we do." The pressure to move it in the event of getting a dedicated national stadium would be immense and probably economically irresistible. But it would be the wrong thing to do.
Incidentally, the Ricoh would be a starter on paper, but I suspect a hostile bid from a third party (the RFL), doesn't figure anywhere in the Coventry City fans' rescue plans, so it might be affordable, but I guarantee it would be a public relations disaster in the city itself (and one that promised not to go away any time soon).