Maybe I am the reason our dues keep going up, but I call MS all the time and ask them to look up availability of dates even when I don't plan to reserve those dates during that call. To me, it isn't worth the effort to post a notice that you want to rent or transfer, or to cancel an existing reservation, or look for an airline reservation, or discuss a trip with the extended family, if the dates aren't even available.
Of course, just because the dates were available when you first called, doesn't mean they will still be available later when you round up the points (or confirm the airline tickets, or talk to extended family, etc.), but you have to start your planning somewhere.
Best of luck -- Suzanne