Yes you can, food can be stored! At a later date less food can be consumed with no work was needed to harvest it.
> Paying for twice the amount of food does not make you live twice as long.
No but using your acquired food (read capital) to trade for medical supplies will increase your longevity. And it will increases the doctor's because he gets to eat!
> If you subtracted all that value spent on basic needs there there still would be a lot of capital flowing around.
Yes and isn't it wonderful? Its what allows things like food stamps and vacations to exist. Excess capital allows things like scientific research to occur.
> ...the rest for social-value-signalling.
That's a pretty pessimistic view of wealth.
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I think I've been pretty realistic in my assessments of capital and its uses. But now, I'm going to enter territory where I'm wildly speculating.
I don't believe post-scarcity can exist or should exist. I don't believe it can exist for two reasons:
1). There simply is not an infinite amount of energy and matter (but there may be enough that it doesn't matter that its finite). 2). Even if there is enough resources, time will always be the limiting factor. Time contributes to scarcity the same way money does.
I don't believe it should exist because I believe that is the end of human progress. Scarcity, whether its a desire to own an iPhone or to acquire knowledge of quantum gravity, motivates humans to achieve.