I strongly suspect that when people talk about regressing to past lives (which I don't agree with, we are all unique), they always go for the famous/glamorous historical figures. I've yet to come across someone who claims they were once a peasant! And in that I think there is a certain amount of wish fulfilment. To be as glamorous as Cleopatra, as powerful as Elizabeth I and so on - there's nothing to wish for in being a peasant other than to stop being one!
So what do your characters wish for and why? In a magical setting, what wishes can't be granted and why? What is the equivalent of a peasant in your created world and is there any sign of improved conditions for them? (I am certain I would've been a peasant and, knowing what I do now, would've hated being illiterate).
If your world allows time travel, how does it work and does it take its toll on those using it? (I think there should be a toll, likewise using up too much magical energy drains those using magic. Whatever the resource, there has to be a price paid somewhere for using it).