Do what you said in your letter: Pack the house with members as well as supporters of the Clubs that use that facility, including teens and pre-teens. Have a number of well spoken adults as well as the younger attendees sign up to speak before the council. Have at least a few of the adult speakers make it known to the council that the adult members of all these clubs/groups are registered voters (do not assume that they assume that, always best to point this out to politicians). Invite the media to attend this "Important Meeting" and speak to them before the meeting so they have your side of things first. As each speaker addresses the council, present your side in an organized, thought out manner.
You CAN get things your way, you just have to present it in a way that will seem to make sense to the council as well as how it benefits the community (can help at-risk youth, after school programs, etc, etc - even if some of these programs are only in the planning stages). Be creative but make it all sound like worthwhile benefits to the community.
You don't think developers and others that want the council to vote their way do the same thing? Its politics.
I know, I've gone to many meetings in the past and have addressed councils and committees. The better you make it all sound, the council may like it also because they can then say they support these benefits and the positive role you all are doing for the community.
Anyway, that's my suggestion.