Do you have proof for this? Everything I've ever seen says that floppies see little to no increase in readership when a show or film hit, with the extremely rare exception like Guardians of the Galaxy. Trades apparently see a nice spike, but only for the short term.
Not calling you a liar or anything, just curious if there's a study out there with contrary findings that I haven't seen. If you have a link I'd love to research it. I study business, so, y'know....I enjoy weird stuff like this.
Oh, there's no chance of Kara not being Clark's cousin, at least for the foreseeable future, but conceptually it's always been a terrible idea in my mind, even when Kara herself is well written and enjoyable. Just say she's a Daxamite or something, is what I say. They're vaguely related to Kryptonians, there's your "cousin" connection right there.
If you were to mess around with Cir-El's origin a bit, why not tie her into the 31st century? Superman has always had strong connections to that era (even post-Crisis eventually brought those back) and you could say that Cir-El was sent back for some critically important reason, if only she could remember what that is.....