Here is an interesting article in the Seattle Post-Intelligencer on a decline in the Mariners' on the field fortunes, and it's effects off the field. Some local businesses are feeling the impact:
Game day sales at King Street Bar & Oven this season are about half of what they were last year, said Anderson, who bought the restaurant with Christy Schatz last summer. Instead of serving crowds hours before a home game, they're lucky if the restaurant fills up an hour before the first pitch. Because of the decline in sales, Anderson cut his staff from two bartenders and three waitresses to one bartender and one waitress on game days.
Note: that fans aren't spending as much on the Mariners and complementary goods does not mean that they've stopped spending entirely. If that were true, one could detect a cyclical impact on the overall economy in smaller cities (like Seattle), as the record of their teams goes up and down over the years. To my knowledge, no study has ever documented such an impact. Brad Humphries did find a small Super Bowl effect for successful football teams, but the emphasis should be on "small," and that finding stands in contrast to most of the evidence produced by academic studies (including Brad's).