If there is a purpose behind reincarnation, it would seem that establishing some consistency in our experience, body type, identity and personality would enable us to focus on our purpose. This consistency could be evident in the number of cases in which people resemble past life personalities and exhibit similar traits. Of course there are clear examples in which people choose quite different appearances and situations, perhaps because their purpose involves exposure to a unique view of the situation.
I would equate both situations to someone in this life who is trying to solve a technical problem where they repeat a formula or technique with only slight variations each time. Then, by suddenly leaving their laboratory and going for a drive in another part of town, the solution appears as if by magic. Both are important, but 90% of it involves perspiration and 10% involves inspiration (Thomas Edison).
In the case of reincarnation we may spend nine out of ten lifetimes repeating similar lifestyles preferring the same sex, appearance and personality with only slight variations along the way; then spending the tenth in a totally different situation which enables us to achieve some great insight.
This is, of course, an over-simplification of what probably takes place. And I do think that variations are as plentiful as the number of souls. But I also suspect that we experience multiple incarnations in much the same way as we experience this one life that we are most aware of. In other words, if we are creatures of habit in this life, we may also be in other lives as well; thus choosing situations that we are most comfortable with. And, if we are prone to being spontaneous, we may tend to choose incarnations in situations that are wildly different.
As far as being doomed to some type of life that appears to be most dominant in the world, I don't believe that we are thrown like dice onto some sort of gambling table where statistics determine probability. I think that our lives all have purpose, and our choices determine where we'll end up in the next life. Just because the majority of people in the world live in poverty, doesn't mean that we will necessarily end up there.