It's been suggested in a few places that past lives should be examined further. Considering that Epic Destinies do diminish the value of reincarnation to some extent, it seems fair to add more reincarnation-related rewards.
For those of us that choose to master a specific class, by taking all three past lives, there should be some incentive to make reincarnating a more interesting feature.
I propose two different suggestions that either enhance the epic level experience, or reward us for mastering a class' passive past life feats.
1) (a) Mastery of a class should reduce the cost of changing a destinty sphere by 1 Fate Point, or (b) connecting to another destiny by 1 Fate Point.
Something like this is intuitive and would be a welcome addition to any build. It also provides more balance than simply increasing the amount of Fate Points.
2) Master of a class will grant additional passive benefits.
This would also be welcome, but probably is far more complicated than the first suggestion.
Examples: 3x "Past Life: Wizard" would passively increase all spell DC by an additional +1. 3x "Past Life: Barbarian" would passively increase HP by X amount.