Not being a professional economist, I nevertheless present in this short blog post of a reason for having people rich is better for economy.
This reason is that when distributing risks between a several entities, it is preferred that richer entities bear the risk.
For example if I’d be proposed to receive $1000000 (million USD) with probability 20% or receive $100000 (hundred thousands USD) with probability 100%, I would prefer the second, despite then mean value of the first offer is two times better. This is because a million is not my urgent need.
Having more money, I would be able to create some (probably not many, such as 1/2, but this is a general principle and the exact sum does not matter) new jobs and/or invest and/or buy some goods so supporting the producers.
So I choose risks in a way inefficient for economy accordingly basic economic laws (it is however efficient, because having more money I’d have more time to volunteer).
The conclusion: Risk distribution is one factor which makes richer people better for economy.