I don't buy into the affluence VS battler mentality.
It stands to reason that approved foster parents may generally be better placed to care for at-risk children ... better placed in the sense that they have room to house the at-risk child, they have a clear criminal history, they have no allegations of child abuse against them, they can feed/school/clothe/nurture the at-risk child, a parent may be able to afford to stay at home and care for the at-risk child so they have constant stability ... etc etc.
imo
That's up to you obviously, I would just like to expand.
IMO
There's 2 separate issues really. 1. Their appropriateness and capabilities as foster carers 2. Their influence
There's the practical aspects which you clearly state, that many people, battler to extreme affluence can fulfill. (Given battlers can go without to stay home and there's a small allowance).
However the influence the extremely affluent have may be able to blindside the department on their ability, or lackthereof, to deal with the more emotional aspects of foster care.
And the extremely affluent lifestyle may be unable to prepare you for the constant demands of small children. If you've been a manager and think you know what demands are because of that, say. Especially over 35 if you have no experience nannying.
The lack of realistic expectations. And not knowing how to deal with extreme frustration, having not met with that kind of stress, could be just as strongly risky to a kid as an obviously unstable person. Or they could be hiding intentional controlled abuse which could actually be kind of worse in a way.
Not to nitpick, but yeah kids going into care usually don't find OOH care to be very stable, they mostly want to go home.
Just speculation in general.