If we consider HL, tomes can be interesting as rewards but since most people use fates for leveling, the problem remains at lower levels.
Somehow, the current idea in ShB to add tokens is not that bad but still we don't see many players doing them. It was the rush at the release but since, there are less people, only special fates are still some kind of incentive. Low level maps are often ghost places. Currently with the free login campaign, there are more people but it will not last.
Maybe some kind of mix between Kupo tickets and fate tokens could create some kind of incentive. Rewards could be dyes, minions and these kind of things. Nothing big but collectibles or glamour elements. They need to avoid to kill the PotD and the HoH... they would need to create specific rewards at the certain extent. They also need to avoid to repeat the mistake from Diadem with pink stuff.