The relative size of the two classes seems to play into that. If you've got a vast population of subsistence farmers who're suddenly empowered to buy Levis (a privilege previously available to the much smaller population of city-dwelling workers), the resulting economies of scale will be fairly dramatic once the dust settles; but if the two groups are closer in size, increased demand will probably drown out economy of scale unless it's close to some inflection point.

The current situation in the First World is closer to the latter than the former, whereas the socialist and progressive movements of the early 20th century generally happened in an environment closer to the former than the latter. I don't have any actual data showing a causal relation here, but it seems plausible.