I issue a Challenge every few months or so, with a small prize for the winner (chosen by voting with dried beans!).
You could change the voting to using coins of a small denomination, 1 coin = 1 vote, and that way you can also use the voting as a small fundraiser (towards christmas party?) if you need/want to do fundraising.
Auctions of surplus sewing goods and or books, to encourage clearouts can be fun but are best held every other year, rather than annually (held after an AGM works well). And magazine swap sessions with a Stitch and complete what you are working on/WIP/UFO evenings.
Show and Tell - about 6-8 people bring an item along and talk about it for 10 - 15 minutes can be really successful and also brings in ideas of future things to do, as you will probably get a 'how did you make that?' reaction to some of the pieces.
The best way of getting feed back of what techniques people would be interested in trying is to ask them directly rather than asking them to write their ideas down on a piece of paper, but try and get some helpers with this, I presume their is a committee, and don't worry about revisiting old ideas, it is nice to have a chance to re-do some things as you will do it slightly differently each time.
I forget which show it was on (possibly in series 6), but there was one where the guest had a 'book' of small quilts, but they didn't all hinge in the same direction, one would go left to right, the next top to bottom etc. that could make a fasincating project! but probably worked on over several sessions.
Rosemary