A couple of thoughts:
Second week of Sept is one of the lowest-use
DVC times ... if you book at your 11-month window, I can't see that there would ever be all that much of a problem getting your reservation...I've never even tried to book a grand villa, altho I read here that getting one can be difficult...but it would seem to me that in the second week of Sept your chances should be pretty decent, especially at the bigger resorts, even if you don't call right when your 11-month window opens.
Another thought: we've been told over & over that MS won't talk to a non-member...and MS is the only way you can book a DVC unit...so if you called MS, they wouldn't have talked to you (unless you've already joined)...if you called CRO (regular Disney) whatever they might say to you about availability would be completely irrelevant to whether a DVC villa of any size at any time might be available...CRO and DVC inventories are totally separate. So are the CMs...so good or bad service at one means nothing as compared to the other...
Don't know about your guide...ours always calls back promptly, but each one is different...but guides are strictly sales people; they aren't part of the reservation system, so their knowledge, while "insider," wouldn't necessarily be anything more than "probably/maybe/possibly" type advice...they can help get an initial reservation which is a condition of the sale...but they don't have anything to do w/subsequent reservations...that's all MS...
Having said that, in my experience, DVC CMs wouldn't get the same very high marks I'd have given to CRO CMs...maybe it's just coincidence, and maybe it's different now...but two years ago, when we first bought into DVC, I noticed how much less friendly/helpful the DVC CMs were as compared to the CRO CMs...not that the DVC CMs were unfriendly--they were fine--just not as "we'll do anything for you" service-oriented as the CRO folks were...now, tho, I haven't called anyone but MS for two years and I know considerably more about how to work the DVC system so the DVC CMs are just fine...some are friendlier than others; some are more knowlegeable than others...but they're all at least just fine...
I've never tried to leave a message for a call-back on reservations, tho...didn't know you could! We have experienced times (both at CRO and at DVC) when the call centers are so busy that busy signals and lengthy wait times happen...
Final thought: I read these boards multiple times each day (like everyone else, I'm a Disney/DVC addict!) and I see a LOT of comment on how difficult availability is/is getting. That has not been my experience. True, there are times when you might have to use a waitlist, or take the resort that's available...but I've never ever not gotten a reservation...and we've done or reserved 10 trips since joining DVC (boy that sounds "bad!" Told you we're addicts!)...we even got a five-day in-the-same-villa reservation at Old Key West for spring break week (one of the three busiest and "most expensive" (highest point charge) times of the year) only 10 days before we went...I had to "work it" a bit...and went into it not "expecting" it to work out...but it did...the first year, we bought in late June and called for a T-giving reservation--had to use the W/L, but we did get it (w/out the help of our guide, as I didn't know I could use his help!)...so while you do have to be aware that especially for busy times (and perhaps for limited villas like grand villas) you might have to use the wait list, or be flexible as to resort choice, by and large I have found that availability is nowhere near as difficult as I would have believed simply by reading the posts here.
Good luck w/your decision...
