It seems more to me that Marvel is trying to pull in demographics rather than those demographics being key buyers at this point. A lot of their titles meant to sell to these demographics aren't really lighting up the charts unfortunately, even when they are well written. Pandering to specific demographics will just end up with new stereotypes like we are seeing with the female Thor. It's all a matter of writing, just make three dimensional characters that just happen to be muslim, or east asian, or female, or gay, or whatnot, but making these pieces of characters' identities being the sole point of their existence is not creating human beings, but caricatures, people are more than some aspect of them, more than being members of a sociological or scientific group they are a part of by being born into them or unintentionally becoming part of them, etc. Create individuals and build up relations from there, and people will read about those characters not because they are an aboriginal, or have bi-polar disorder, or Brazilian, but because they are good characters that readers either just like to read about or can relate to due to their personalities.
It looks like the two bolded portions of your post don't agree with one another. At one end, you say that if they just write quality comics, people will read them. At the other end, you say titles they hope will appeal to new demographics tend not to sell well even when they are well-written -- which almost seems to imply that they shouldn't bother.
I'm not going to accuse you of being racist, as you probably meant all of this in good faith, but,
as I mentioned earlier in the thread, comments like this, even when said sincerely, are not constructive. These are the kinds of claims racism gets hidden behind. Remarks like "I have no problem with diversity in representation, but ..." -- and it's when you find yourself constructing a sentence like that you're probably feeding into racism without even knowing it.
There are only two ways that sentence ever gets finished. Sure, the precise wording may differ here and there, but it comes down to either "... there needs to be a good reason for it" or "... I just have a problem with how they're doing it." I've already gone over the former, so let's look at the latter.
These claims that "I don't have a problem with diversity, I just have a problem with how they're doing it" ring shamefully hollow. The reality becomes that there really isn't a way the claimant is actually going to be satisfied with it.
Any attempt at diversity gets labeled "pandering" from the outset if any attention is called to it. Meanwhile, Tony and Steve can be featured on everything from Duck Tape to soft drink cans and that's just "merchandising" and "promoting." God forbid, though, that a comics editor goes on CNN for a few minutes to talk about a new racial minority character or a new female character gets announced on "The View" -- a show the prevalent demographics consuming superhero comics aren't likely to be watching anyway.
Nope, that stuff's pandering.
You'll even have folks acknowledging that Marvel is a business and that it makes sense for them to try appealing to more demographics -- but, again, "I just have a problem with how they're going about it." Seemingly, the only way it could get approved is if they create characters who "just happen to be [insert minority]" and then make no effort to actually promote them for their business purposes. Apparently, resigning the effort to failure from the start -- in other words, the promise that the deviant will disappear and order will be restored -- is the only acceptable way to go about it.
That's not even getting into the confusing notion of whatever "just happens to be [minority]" is supposed to mean. I'm pretty sure all fictional characters, including the White males, were created by someone who came up with them and decided on each of their attributes. No fictional character "just happens to be" White, Hispanic, gay, straight, etc.
If you're confused, by the way, as to how the contradictory statements "I have no problem with diversity as long as there's a good reason for it" and "I have no problem with it as long as they're creating characters who just happen to be [minority]" are
both the go-to racism/chauvinism defenses when condemning attempts at promoting diversity ... well, you're not alone. It is quite the intellectual quagmire.
This is why we have a problem. On sight, any hint of losing exclusive privilege -- not the privilege itself, mind you; just the exclusive access to it -- is always (seriously, always) greeted with an angry knee-jerk psychological reaction by the historically more privileged. Then, instead of acknowledging it for what it is and trying to work through it, the whole thing gets denied and covered up with notions that whoever is bringing diversity into the matter is the actual bad guy because they're doing it wrong -- again, whatever that means.
That reaction is probably some evolutionary, biological mechanism doodad or other, but we have a responsibility to own up to it and be better than that.