A slew of articles from major business journals like Business Week and Forbes are available online. All show that sales per square foot are off nearly universally and that predominantly mall based pennants like The Limited are closing, along with many outlets of major anchors like Macy's, Sears, J.C. Penny, etc. The decline in sales of other prime mall outlets like Barnes & Noble and the closing B. Dalton and smaller booksellers as well as places like The Sharper Image have seriously affected mall income which is significantly based in percentages of sales.
But the biggest issue is the rise of online shopping. Read the articles that show that smaller, high cost per square foot mall stores can't have the selection of online stores and younger generations are forsaking them in droves. Add in the already crippling effect of the Big Box stores going back to the first Best Buy and Toys R Us and we just don't see the sales of even two decades ago.
The best indicator is to ask, "How many new malls are being built". The answer is "practically none".
And that is in many cities, large and small.