There have been a number of collections of the ads themselves over the years — a book called Hey Skinny! reprinted ads from the 40s to the 60s and is still be findable on Amazon. But I'm not aware of any academic looks at the advertising itself -- certainly not detailing dollars earned from advertising. Old media kits do detail what the publishers thought their demographics were — or, more often, wanted advertisers to think their demos were. Late 1990s media kits pretty regularly overstated the youth of their audiences — at least, the ones I saw did.

As recently as 2000, Marvel's advertising was available in two packages -- the "junior" and the "senior" line. You bought into one book in the line, you got them all. I remember seeing the list and wondering how they determined what went in what group — it seemed kind of arbitrary. I may still have that list in my files, but I have no idea where it would be. It is certainly the case that that "bundling" was how publishers generally approached advertisers — back in the 1940s and 1950s, you'd see listings in the Audit Bureau of Circulation files not for single titles, but for multi-title groupings within some publishers — frustrating folks like me looking for title-specific data.

Something not to be overlooked as well is the importance of "pass-along readership." Publishers' ad reps always touted this as a specific virtue of comics, and I am certain that it is. A magazine ad might have a pass-along readership of 1.5 persons per copy, whereas a comic book would be expected to change hands many times, exposing multiple readers to the same ad. Now, it is possible that the churn rate has changed over the years, and that pass-along is no longer what it once was for new copies -- but I'm on record several places as saying that the 1970s Hostess comics ads, dollar for dollar, may be among the best ad buys in any medium, ever; the product still exists and the original ads are still being seen, years later. They're part of pop culture, like the Charles Atlas ads (from which "Hey Skinny" got its title).

One thing you can observe is ad placement practices over the years. Marvel reached a high of 15 pages per 32-page issue in the late 1970s; that was way too much, but during a time of huge inflation; ever since, they've mostly been down to 10. DC tried half-page ads in the 1970s, splitting the comics pages in half; no one liked that practice, and it went away.

There have been other experiments. Dark Horse experimented with putting all the ads in the back in the 1990s. Marvel did a direct marketing test called Marvel Mart in 1994, selling its own merchandise directly; comics retailers balked at that, some ripping the catalogs out of issues before they put them on sale. And Marvel did a test not too long ago essentially adding another signature of ads to some issues but not raising the price of the comics; fans weren't crazy about it and retailers objected to having to pay the extra shipping. Ditto for the wave (thankfully over) of AOL and other CDs that were inserted in comics.

That's off the top of my head, but those are some of the issues involved. Good luck!