This looks like it'll a long and interesting thread and I hope my contribution helps.
1. The majority of people are middle class or poor. No doubt there would be DROs who service only the very rich and have clauses about protection from stalking, kidnapping, alien abduction or frizzy hair, but most DROs would not find it profitable to focus on small percentages of the population.
All purchasing power means is that someone can buy a big house, expensive cars, yachts and shit like that, it does not mean that they can, in a free society, rule over those who have less capital.
In our current statist society things do indeed work that way, so I can certainly empathize with that concern, however misguided it is.
An analogy that might help is the auto industry. The rich can afford to buy cars that are more expensive and the auto manufacturers profit more (we'll assume for now) from the single sale of an expensive sports car then a cheaper midsized sedan or budget compact car. But what do we see most in the market? Sedans and budget compact cars. That is because those cars, even though there is less profit made from selling one of those, so many more of those are sold over the sports cars, that it becomes more profitable to market to the poor and middle class, hence why Toyota and Honda are as big as they are.
2. It helps to have statistics that show poverty going down before welfare and then going up after welfare and increase in charitiable donations when taxes decrease, but there will always be counter arguments and statistics to that that are on equal standing as your statistics and counter arguments. So, IMO, it's best to approach this one with the argument from morality or to let them prove to you that it is just to steal from everyone to give to a small group of people or that it even helps lift them out of a poverty we assume they do not want to be in.
3. Freedom as compared to what? Freedom to buy a Ferrari Enzo?
4. The sentence in the parantheses is a universal criticism, something that can apply to everyone in every instance. Everything and everyone has it's/their own advantages and disadvantages. To take a simplified and possibly overused example, the rich have a lot more money but they also have more responsibility while the poor have less responsibilty.
In regards to the unparanthesesed part of that, you could also respond by pointing out that while that may be true, it's invalidated by the fact that the person asking that question believes the same thing. In some idealized Marxist society (esp. from those who haven't read Marx, like myself) of perfect economic egalitarianism, there would still be a ruling class who would excert far greater power than Oprah excerts over her mass of wailing sit-com stereotypes (AKA viewers).
5. The burden is on the person who makes this point to demonstrate how purchasing power limits consumer choices.
I'm curious, why are you a market anarchist and how did you come to that conclusion?