Whether Kikuchi's mainstream exposure translates into benefiting Idoling's brand status and popularity remains to bee seen, next single may be a good barometer I suppose, but it's one thing for Kikuchi to be liked by the various TV show staffs and getting the invites, it's quite another for Kikuchi to be claimed as a household name, I don't think she's there yet. I would say Kawashima Umika of 9nine is known a lot more in the mainstream than Kikuchi is, but 9nine is no where near the popularity level that it should have with Umika as a member.
No one member should be pushed that much at the expense of the whole group, that's just not Idoling-like. And let's not over-value Kikuchi's MC brining out other members' personality thing, there are plenty of other segments where members' personalities are showcased even stronger. Take Miyake for example, the only impression I have of her in any Ami-talk segment is her just talking. But in other segments I've seen her cry (candid camera), hop in joy (2 point last place exam episode), lose her cool (scolding Yuna), overjoyed (Valentine cake winner), showing off her flexible joints frog leg style (hip circle), talking like a baby (fansama request), among others that are far more memorable. Ami-talk segments for the most part are bland and trivial but they keep doing Ami-talk, how is that a good thing to keep doing low quality segments?
Believing whether it's the self-promotion of Kikuchi or not is not the issue, but it's very clear that promoting of Kikuchi is the intent of the staff by featuring Ami-talk so frequently. Not only is that a bad thing for the whole group's dynamic, they are sacrificing quality for 15 minutes of fame as most Ami-talk segments are boring.
I honestly don't feel that the leadership position is a matter of concern, I don't take much stock in it. But age-wise Kikuchi is not young either at 21 becoming 22 this year, in fact her looks have deteriorated quite a bit over the past year due to fatigue I suppose. But considering that Maipuru will name the next leader, I would be shocked if she picks Kikuchi. But I sense that the staff will intervene in some way and make Kikuchi the leader somehow because the staff is a sellout at this point and anything for 15 minutes of fame stance of theirs.
For the sake of your sanity, stop over-valuing Kikuchi's character, talking skill is not a necessity for an idol to become popular, AKB's Maeda Atsuko doesn't even talk much and she's the all-time center.
As far as variety goes, I would put Asahi on the top of the list, I can't quite describe what it is about Asahi, but she's just hell a lot funnier than Kikuchi ever could be. On the next-tier would be Maipuru but she's more of a MC-type, Tachibana is quite talkative and funny and a better all-rounder than Kikuchi, Kaede by herself is quite entertaining, but with Ruka combo they are incredibly funny. Umeko and Sakacchi are just too specialized, and they have a tendency to disappear in away outings. I sense that Yuna is trying very hard to go to the front, but I'm not too high on her.