What If Investors Won't Join the Party?
Gretchen Morgenson column says economic rebound in US is threatened by continued depression of broad stock market indexes, which generally begin to rise well before evidence of economic recovery; says that if stocks stay in slump, consumers may rein in their spending, hurting recovery, and that prolonged slump would make it harder and most costly for companies to raise capital they need to expand their operations and increase revenue and profits; suggest that fault lies in good part with steady stream of accounting scandals, corporate chicanery and questionable practices at Wall Street firms, which are undermining investors' trust in nation's capital markets and role they play in helping to generate growth and prosperity; photos (L)