Yeah, in less developed countries, the system would never improve, but I would still argue that, at least in an reasonable idealised approximation, the "average" standard of living in the west wouldn't decrease (or if it does, it won't be unsufferable). I can also outline a procedure leading to an increase in standard of living that doesn't involve invention (i.e. entrepreneurship, which is undoubtable stifled under communism), just innovation (which is commissioned internally in a company).
The flexibility, IMO, would be in the supply (much as it is now actually). In general, prices are determined by the cost per unit of production. The price per unit of production is in general fixed (and this is even more the case if everyone must be paid $11,000 p/a), and the demand at that price is met by the number of units produced (i.e. the supply). So if the price per unit of a good is decreased by lower wages, so too will the prices (this would fall in line with the deflation caused by assigning a higher value to the dollar). Circularly, the price of the raw materials required to produce the goods will also fall, further reducing the prices in line with expectations based on deflation. But we already knew this.
In general, prices increase when the cost of labour increases and decrease when the company increases efficiency per unit of labour. Assuming this is true and the only truth, lets say demand for a particular good increases. An increase in demand would lead to an increase in supply, which would lead to an increase in profit without an increase in prices. The company can now invest in improvements that would increase its efficiency, which means lower prices. Lower prices means people can buy more stuff; more of our company's stuff, or more of other company's stuff, i.e. an increase in demand for goods from other companies. These companies experience similar effects, and similarly invest, and similarly reduce prices. Thus the standard of living can increase through an increase in demand for a certain good.