There would be no more sure, instantaneous way of bringing about the collapse of the American economy than means testing Social Security.
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The effect on demand depends on where the means test is set and how it is measured. It would not impact the spending of the wealthy at all. If they have 1 million a year income, SS isn’t impacting their lives at all.
Also, you are implicitely using a Keynsian analysis: aggregate demand goes down and that is the problem. The Austrian economist will say that when the economy is in recession there has been a misallocation of resources and government needs to downsize and reduce taxes so that private enterprise can reallocate resources more efficiently.
Your explanation does nothing to overcome the fact that, at the margin, means testing Social Security would provide an economic bounty to stop producing new wealth and to squander accumulated wealth.