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Discounts for renewing members, but to make it fair for long term full paying members rather than them having a cheaper membership, how about reducing membership cost & games? for example (plucking numbers from the nowhere) year 1 = 8 games @ $200, year 2 = 7 games @ $175, year 3=6 games @ $150 etc? Keeps them members and they can always go for a full membership again anytime.
Custom memberships - essentially pre-buy tickets for games they want to see for the whole season, and get membership benefits. An individual would be able to create a custom "Force -v- NZ" membership where they only have tickets to matches against NZ teams.
I know there is a "Family Stand", but if you want to engage kids, you need to target them - a "Kid Zone" section where you can focus on them. Players spending real time there and/or an extra few minutes post match, free soft drinks (a free coffee for parent?), kids toilets, free stuff for all like boom sticks and give aways such as balls, maybe an extra security guard who's role is to keep a gentle eye on the young ones. you could allow any members/ticket holders with kids to use this section, but would need to keep it small enough to manage. 1st come 1st served?