A smart way of keeping people active would be the ability to mail your entire downline of referals which one message.

(Not  private message or they won't get it being offsite). If you added an internal system to mail them all (security first of course). Members who have created accounts but forgotten the game, etc.. would likely login much more often to play.

This would also be great for the referral contest to remind new referals to play so they can become eligible for counting (level 2)

2 cents