I think the girl scouts would definitely make more money if they used regular retail channels, but I can't be sure. They ABSOLUTELY would sell more. Demand for girl scout cookies is not driven solely by the fact that they are rare. The demand comes primarily from the fact that they are so damned good. I simply do not buy any other cookie. Period. Which means I buy cookies exactly one time per year. Thin mints are the best cookie on the market. But, beyond that, they have a bunch of other varieties that are better than anything else you can get on the store shelves. If the Girl Scouts put their product, which has plenty of name recognition, in the grocery store they would go toe to toe with Nabisco any day of the week. It's not just novelty. They peddle the best product on the market.
With that said, they need to do more than just sell more at retail than they currently do in order to make it a good business move. They need to sell enough more to make up for the fact that they currently don't have to pay for shelf space or otherwise give the retail store any sort of kickback. And they have loads of volunteer workers that peddle and advertise the merchandise for free.
But in the end, I honestly buy the reasoning offered by the girl scouts. It's not just about making money for the organization. It's (also) about the experience, and feeling of accomplishment it offers the girls.
BTW, some interesting trivia: The Girl Scouts as an organization have absolutely nothing to do with the production or even the recipe of any of their cookies. It's not like you have this grand-master girl scout who is a brilliant baker and developed all these wonderful recipes. They just paid another company (a company that has developed lots of cookies that are sold at retail) to make the cookies for them. The only thing the Girl Scouts do, or have ever done, is branding and selling.