It's not just music that determines the fate of an idol group, to be honest I don't think music itself matters that much, maybe 10% of all the factors. It's just that Idoling used to have very good music for an idol group aided by the fact that they actually have very good vocals and unique songs that also used to utilize the vocal abilities.
The biggest problem I see in Idoling from becoming a hit is really marketing strategy or lack thereof, and incredibly bad timing. In my mind Maipuru should've been given at least three solo or duet songs in the album CDs by now, and should've had a solo concert 2 years ago, the staff has totally missed the opportunity to fully take advantage of Maipuru's talents while she was still young. The same could be said of Rurika more or less. The lack of promotion and development of the individual member in the right time just never seems to materialize until it's kind of a bit late and have the fans wondering why the staff isn't being proactive enough.
They are making the same slow reaction with Asahi more or less as well, Asahi was much cuter when she first joined Idoling, she should've been pushed 2 years ago instead of now where she's not that cute any more and no longer a magazine model, a little too late.
I'm not advocating that youth is superior, it's just that the peak period for an idol tends to be when they are younger rather than older. It's much easier to get attention with just looks at a younger age, when an idol goes over 20 years old looks alone simply won't be as effective. What the staff really needs to do is specialize the roles for the members that tailor to their strength AT THEIR PEAK PERIOD. Instead of simply putting Asahi, Maipuru, Yuna, and Aichan in every PV scene possible and having the subpar vocal members singing the coupling songs which yield unimpressive and less than ideal quality in the outcome, have the younger members with looks to represent the youthful PV with Kaepyon, Karen, Ruka, Yuna, Kurumi, then have the vocalist members belt the lines for the main vocals and that formula would produce a much more visually sensible PV and a spectacular sounding song.
The fact that Morning Musume managed to double the single sales from last time isn't because of the song itself, but because of the super-extra promotional efforts, and it seems like they have jumped on the hand-shake event tactics as well. Tsunku is very good at promoting the younger members at the right moments, although I feel that sometimes they are being pushed way over the top, but at least the younger members get their share of the spotlight instead of being shoved into the background for 2 years or so like Idoling does. When I looked at the comments on YouTube, Morning Musume is getting new fans by watching the younger members, not Michishige.
While there are many faults to be found in Idoling's system, what I find very worthy about them is that their chemistry with each other is one of a kind, there's a genuine quality to it that simply can't be found in other groups. And there's no question in my mind that Idoling is the funniest idol group of all, it's a shame that the Japanese public and the idol culture simply don't hold humor and comedy very highly in the idol industry.