In the End of an Era thread, @Amethyst said:
Instead of being bought, Ace Membership will be gated by account age and a new feature called EXP (it's exactly what you think).
EXP will be earned by contributing positively to the site, including earning reputation, helping others in need, and helping to keep others in line.
EXP can also be lost when you receive warning points.
It may also be worth mentioning that this EXP system will be available to users who primarily use the server only (unlike our current post count requirement, which has been removed), making it practical for them to get ace/voice too.
Edit: I've also heard that the Samaritan's Speaksay has awarded a large amount of exp to people who are written about in the positive feedback that is submitted.
Along with this, it's mostly up to the forum authorities to decide whether or not you gain EXP or not. Sure, you could be helping a lot of people in some way, but if an authority does not see it or does not think your action is worthy of EXP, then they will not award EXP to you.