I think, like the Council, there are a few people kidding themselves here. You can go and look at the stats for yourselves...
http://www.premiershiprugby.com/matchcentre/fixtures/fixtures.php?includeref=9229&season=2013-2014
The only team that get anything like 'decent' attendances by football standards are Leicester Tigers. And then you've got Saints, Bath, and Gloucester - who are closer to 10,000 generally.
And these are well-established teams in places that can genuinely be called rugby towns. We've got a franchise team, moving into a town that's primarily football, and who have already p*ssed off a reasonable number of both the local rugby and football fans.
As for having Brum (say 2m people) on the doorstep, Wasps had London (say 10m) on theirs at Wycombe, and could still only get 6,000 or so.
My prediction is that Wasps might get a lift at the first few games through novelty and freebies - and they'll get big (c20,000) attendances for Saints & Tigers games, probably, but the majority of games will be a few thousand. They will be lucky if they get as many as they got at Wycombe, imho, and I don't see that changing much even over a longer period.
It's not much fun at the Ricoh when it's three-quarters empty, as we know.
Where they might make money is on the corporate side. Rugby traditionally does quite well on that front, and the Ricoh is well set up for it. It's hardly likely to bring a vast revenue into the city as a whole though.