First of all, my doubt is not about sales but her as an artist that capture my heart.
I'm sorry to say this but I do kinda tried not to get into her music too much lately, mainly because she's been in the industry for quite a long time and it won't be long before she announces her wedding and stuff, and very likely she'll step down from her J-Pop queen's crown when the time comes. My plan would not have worked though if she keep producing awesome singles and keep me faithfully attached, but the fact that some of her recent work are not as good as her old ones (IMO) makes it easier for me to get away from this fanboyism.
You know, I used to be ONLY into her music and Ayumi means the whole J-Pop to me and nothing else matters. However, eventually I start to think "hey, this is not very healthy, what if she decided not to sing anymore?", and then I started to diversify the J-Pop I listen to and get into more artists and discover a bigger world.
It's the way how J-Pop industry works that makes me doubt her. Nobody last forever in this industry and you can go down really fast, seeing how Namie loses her popularity after her wedding despite being the Queen during the early 90s.
I'm not as into Ayu's music as it used to be, but well that's just me, I still like some of the songs she released lately, but they no longer has the magic compared to her Duty era, which is about the time I get into her music. I still respect her as an artist that brings me into the J-Pop world and I'll continue to listen to her as long as she release something that's interesting. (I hope I"m not depressing anyone with my experience)
The thing I don't particularly like about (miss)understood is that too many songs are composed by SWEETBOX, and yes that makes the album very westernized. I think she should really start composing again using her CREA identity and show her fans what she really got under her sleeves. Songs like "M", "Endless sorrow" can really bring her into the spotlight again and regain confidence of fans that start to doubt her a little. Even DAI's BLUE BIRD has dissapointed me so I guess she can no longer rely on other composer, afterall they're not going to compose the music that she really wanted to do. Nothing beats DIY, right?
P.S. I did buy the limited edition of (m)u so I'm not a factor that affects her sales.