I guess the central premise of capitalism is that while every society has its haves and have nots, capitalism is supposed to encourage the haves to invest in the economy rather than hoarding their wealth. In return, they stand to get even wealthier, but a stronger economy ought to generate more employment and generally improve the lives of commoners as well.

Nitpicky, but that's the premise of Liberalism, not Capitalism. Capitalism emerged not because it was an idea, but an evolution in Mode of Production. Liberalism is the ideological justification.

Unfortunately, in a never-ending quest to make wealth-generation more efficient and streamlined, employment is being eliminated through automation, outsourcing, etc. and the system is eating itself out from the inside. I doubt it can persist much longer, but what will replace it remains unclear. I pray that it will be something sensible that ensures everyone has their basic needs met and can still find rewarding pursuits in life. But there are so many ways it could go very wrong, and that includes staying on the current course.

Have you read Marx? He makes the case that due to Capitalism's tendency to centralize and form monopolist syndicates with internal planning, the next mode of production is Socialism, ie public ownership and planning of the syndicates formed by the market system.