Our church is in a similar situation as Preachin' Jesus. Our Senior Adults use the quarterlies and probably use them for their private devotions at home.
However, none of the other classes are even expected to prepare. Teachers simply present the lesson each week, usually little by little with questions for discussion and application after each point, and when someone says something that one of us teachers thinks is really wrong, our response is measured depending on the seriousness of the error and the contentiousness of the issue...
ie, if someone argues for an alternative eschatological view, we would probably say, "that's a view many christian's hold, and that's fine."
If someone speaks of losing one's salvation, we would likely point to several verses that support eternal security, but then also admit that many Christians disagree.
If someone proposes that Jesus was not really divine and had 5 children with Mary Magdeline, we would likely try to correct it more forcefully for the benefit of the entire class.
We might recommend a book no more than 3-4o times a year, at the beginning of a new series, if there is a book we are basing the lessons on, or that fits well with the topic.
It is helpful to not try to do to much. Occasionally a fill-in teacher will try to do to much, and ends up monologuing for 40 minutes and then says, "Any questions?" At that point, even those who have tried to keep up have so many thoughts swirling in their head that they wouldn't know where to start.
Our Sunday School has been growing in recent years, even faster than worship service attendance. Interest is there, and discussions are often lively, but not in preparing for SS ahead of time. We have not attempted to change that.