I will tell you that even if the economy goes into a depression... the stock market will not lose 80% of its value, and return to 2600.
For one... we have huge institutional investing now... which acts as a buffer. Also.... the Stock Market in 1929 WAS the bubble. The prices were completely outrageous... and earnings compared with stock price analysis analysis became irrelevant.
HOWEVER!!!! this does not mean that our current economy cant go through a horrific depression. I think... the worst is way ahead of us.