Back in 2001, I documented that the share of advertising spending in total economic output (GDP) and real advertising spending per person-hour of media use has been roughly constant since 1925. The development of new sensuous forms of media, such as radio and television, did not change the macroeconomics of advertising.
Google (GOOG) has acquired a market capitalization about $125 billion using text-based advertising. Google has created value in advertising not through media innovation but by making advertising much more information-intensive.
Perhaps such a change in advertising will make possible sustained growth in the share of advertising spending in GDP.