Crossword puzzle clue "one of many seen on a stock car"

One of many seen on a stock car

Spiro who wrote, "If you've seen one city slum, you've seen them all"

"If you've ___ seen a one-trick pony, then you've seen me"

Stock to put stock in

Rumored reason for the stock market plunge of 5/6/10, whose effect is seen in this puzzle's theme answers

Springsteen "If you've ever seen ___ trick pony then you've seen me"

Feeling that you've seen something before seen something before

"If you haven't seen ___, you haven't seen New York" (old ad slogan)