Some simple ideas of which I am sure we have MANY others
1) Any season ticket holder adult can bring up to 3 kids for a quid, they can apply for a temporary seat swap in their area (subject to availability) for each game to allow the kids to sit with the grown ups.
2) Friends for a Fiver - any season ticket holder can bring a student for a fiver (same deal on seating)
3) Mates for a Tenner - any season ticket holder can bring a friend for a tenner.
All new tickets sold only to ST holders and all new buyers must complete the membership application on-line so we can bombard them with junk mail marketing.
Cup Games - all ST holders for a tenner.
I'm sure 'Pay on the gate' would persuade a few more casual attendees but with the advent of crowd segregation I'm not sure how this would sit.