Hi! I really like Rose's idea of a Lego night, and may put that on our list of possible future events...
Frustrated, I have a couple of suggestions about your situation that may not help you now but could help you later. First, your group ought to work out a schedule and budget at the beginning of the year and stick pretty closely to it. Then, when people pop in with special requests, you can either accommodate them if you feel it's possible, or say it won't be possible this year, but your group will consider it for next.
We have our year's schedule lined up and voted on in the first meeting of the school year. The upside is what I said above, we have a plan, we stick to it, and we don't get surprised beyond our capacity. I will say that we don't automatically say no -- we look and see if there's any way we can make it work and if not, oh well. We don't sweat it. The downside is that you have to work carefully not to give the wrong impression to new parents, that you aren't open to new ideas. I don't think we're perfect at that, but we've gotten better, with new parents understanding that great big giant ideas, like new events, may not happen this year, but ideas to improve the existing events are definitely worth a try, and we do try them out if we can.
The teachers may not have a lot of extra time to spare. Some teachers are able and want to give a lot of their free time to the school, but others may be involved in church, hobbies, their own kids, whatever. I think you should try not to feel bitter because teachers don't automatically step up. Keep asking for help, and be thrilled when you get it!