What you've said, Nicholas, is true. MikuNoPolis is a great example of the dedication of the VOCALOID community. Also as you mentioned, we don't represent mainstream.
The actual reason for Miku (when I say Miku, I mean the CVs) not coming back is (a) the 39's band is retiring (whether temporarily or not, we'll see - a sad thing it is, such a great band with awesome personalities) and (b) SEGA is super busy with their NEXT Hatsune Miku Project DIVA for both PSVITA, set to come out this year, and PS3, for next year. Seeing the new models and the new rendering engine it's based on (not limited to two characters at once, as with the old series based on Virtua Fighter), it seems that SEGA will have to manually redo/convert/make-new each and every single module to be used. That's a ton of work - which explains why their temporarily retiring from the concert business, which is also a huge job to handle.
Anime EXPO made an official statement saying that SEGA has other plans but 2013 may possibly hold foreign concerts - presumably after the release of NEXT HM PjD PS3 - you know - for the superior graphics ;D
But it's all in good timing, as English Miku will take much longer than expected (seeing as we it was previously estimated to be released at about Spring 2013, but now Itoh says "by the end of the year"), and the recent FINK demo leaves much to be desired. We don't actually know the full potential of her English because (a) the song was not fit for clear pronunciation, and (b) FINK is not a very experienced VOCALOID user, albeit a known musician (likely why CryptonFM chose him). Even Ballet Mecanique was better. In fact, it BM (oops) showed that Miku is capable of singing English without going the "kawaiiMOEdesu" route - she sounded pretty serious, except, you know "MEER rrr" (mirror) and "skahs" (skies). One thing I'm really hoping for Miku is that she has the flexibility for accepted English pronunciation (like, singing not as you speak - "my" = "mah", or underpronunciation (in contrast, Engloids like Sweet Ann and Big Al suffer overpronunciation)) as well as her classic cutesy voice. The general population tends to go for the former choice. Combine this with a catchy song (as long as the lyrics are English, as you said) and I think it'll catch on. I mean, if people really cared about what the songs in mainstream USA are saying today (drugs, alcohol, [other stuff], etc.), I don't quite think they'd be listening to them. But if we can have VOCALOID bring poetry back into music and get past those "gotta go for platinum label!" or "I'm gonna buy a cake for JB's birthday!" record companies and ravaging fans (respectively, of course ;P), I think we just might start a revolution :D
But until then, what you said. :P