I think one thing that might make a difference in this regard is inclusion in the brew Caskroom list .. I've installed more apps through 'brew cask' than through the Mac App Store, that is for sure, and usually its because I was able to quickly and easily search, locate and discover apps very rapidly with a simple 'brew search' .. its at the point where I consider inclusion in the Caskroom repo's more important than App Store submission at this point. I trust the community software collections a lot more than the 'official Apple' channels, for some reason - I'm sure its not rational, but more just a fear of corporate control and the ultimate denigrating effect it has on the quality of software.
Plus there's the whole 'brew update && brew upgrade && brew cleanup && brew doctor' factor, that gives me - rightly or wrongly so - the impression that I have far more control over the software on my system than that granted me by the graces of Apple.
I use Cask a ton too. But we have to be in the huge minority. No one I've shown Cask to has ended up using it. I'm mainly talking about slightly above average techies or a few people who are comfortable with the cli. I doubt any paid software listed in Cask has their download numbers change by more than a few percent, if that.
Plus there's the whole 'brew update && brew upgrade && brew cleanup && brew doctor' factor, that gives me - rightly or wrongly so - the impression that I have far more control over the software on my system than that granted me by the graces of Apple.