This is my view on this topic exactly. The fact that it is a show targeted to younger girls and their parents that just happens to be watchable by people outside of this demographic is what adds to "magic" of the show's appeal. As you say, if they attempt to shift the show to either side of the spectrum, then it is very likely that the show would lose its charm.
I actually think that this is the reason why Jayson Thiessen has said, several times, that he does not want to change the show's formula too far away from its foundation. They did not necessarily anticipate attracting such a large and diverse audience of viewers. Now that they have, it would be very difficult to isolate which features of the show were essential to making it such a cross-demographic success.
I particularly remember when he was participating in one panel event, and he was asked if he would incorporate fandom stories or other elements. I remember that he replied and said that he would have to be very careful if doing so. His reasoning was that there was a possibility that if he set out to implement elements from the fandom he might actually end up mistakenly removing the very elements of the show that had attracted this fandom to begin with. He all but referenced Suited for Success when he said that fans may love the show but we may not necessarily know what is best for it.
I am reminded of Batman The Animated Series. I remember one day when I was watching a dvd that had some commentary on it from some of the key people behind BTAS (Paul Dini, Bruce Timm, et al). I remember that the guy interviewing them asked them what made BTAS such a success. They basically replied that the show's success was the product of so many different factors that it would be nearly impossible to pinpoint any exact thing.
In that interview, I remember, very specifically, that Bruce Timm said something to the effect that the show's success was a product not only of the show itself but also of the era in which it was written. He would constantly wonder if one day he would wake up and the show would no longer be popular, but it kept on surprising him. He said that, as far as he was concerned, they were just ordinary people working as hard as they could on something that they loved. They didn't expect it to be as big of a deal as it became.
I would imagine that the creators of Friendship is Magic feel similarly. They are just ordinary people working as hard as they can on something that they love. Regardless of how much we may want one thing or another, it may be the case that if the creators of the show stop and try to purposefully refine the show's audience, then the show would lose its appeal to all audiences.