To what extent, and for what duration, was Germany devastated? How did this cataclysm impact Germany in the 18th and 19th centuries? Are its aftereffects still felt?
I can give a decent answer to the question of the cultural memory of the Thirty Years' War, and hopefully someone can cover the economic aspects in greater detail.
The extent of the devastation wrought upon Germany has been the subject of some debate. Certainly the devastation in terms of Germany's population is substantial, with commiserate effects upon the economy. In this light, the devastation is roughly similar to a major outbreak of plague (though, it should be noted, not nearly as extensive as the Black Death of 1348). A new power center, Brandenburg, emerged, having been largely spared from the devastation wrought elsewhere, and being positioned favorably in 1648 to receive and maintain influence in Western Germany.
Interestingly, though, according to Wilson in Europe's Tragedy, the understanding of the war and its conclusion was fairly positive (at least among the literate classes) in the century following the Peace of Westphalia. Protestants celebrated the confirmation of their rights, the Holy Roman Empire was saved and strengthened, and the general positive reception of the Peace of Westphalia has continued unto the present day.
According to Wilson, the war receded increasingly into public memory as the 18th century witnessed additional conflicts. However, late in the century, proto-Romantic movements in Germany (and, later, the future Czech Republic) began to revive memories of the war, rewriting the struggle in national terms as the French Revolution again threw the world into a major upheaval.
However, by this time, the destruction Thirty Years' War was just that—a memory, literary fuel for the Sturm und Drang movement. What had been a forgotten memory of destruction suddenly became relevant, as French armies again marched across the Holy Roman Empire (and ultimately ended it). As German nationalism grew in the 19th century, the Thirty Years' War grew into the preeminent historical war in Germany's history, a defining national moment.
Main source:
Peter Wilson, The Thirty Years' War: Europe's Tragedy
One lasting thing came out of the 30YW, which was the first real definition of the Nation State as we understand it today - the principle that you drew a line around an area on a map and say "This is France. It is ruled by the French King, and its people are French subjects. This over here is Spain. It is ruled by the Spanish King and its people are Spanish subjects - even the ones who speak French. The French King and the Spanish king have no right to interfere in the running of each other's countries.