While it would be rather hard to prepare for, perhaps actually having some "improv" type seminars mixed in with the pre-planned topics might be a good idea. Possibly have the speaker set what the basic topic will be (SQL backups? Statistics? Indexing?) so they can get some notes in order, maybe prep some demos for likely questions.
The attendees then are asked to bring up anything, no matter how small, that they might have a question about related to the current topic. Attendees would be encouraged to offer suggestions and ideas to other peoples questions / issues, and possibly given the opportunity to borrow the presenters' system to demonstrate. Almost more of a "round table" type discussion, rather than the "class room" type.
It would give the newbies a chance to ask questions in an arena with a large breadth of experience, while the "old salts" might pick up something new or be reminded of a feature they forgot about...
Having attended one SQL Saturday a few months back, it did seem there was at least some audience participation, although it did feel somewhat "schoolish." Not a bad thing, and I still enjoyed the seminars.