Millionaire investor confidence rose in March, according to a Spectrem Group monthly survey, even as confidence amongst affluent investors declined.

The Chicago-based research firm announced Wednesday that its Millionaire Investor Confidence Index rose four points in March to negative–six, this represents the millionaire index’s eighth-consecutive neutral reading and follows a one-point decline in February.

Meanwhile, the Spectrem Affluent Investor Confidence Index, which measures the investment confidence and outlook of households with $500,000 or more in investable assets, fell two points in March to negative–12. The index now stands in mildly bearish territory, down from neutral in February.

“The nation’s wealthiest investors expressed mixed opinions on the investing environment in March with millionaires growing slightly more confident, although at a neutral level for the eighth-straight month, while the broader affluent population saw a small decline in its investment confidence,” said George H. Walper, Spectrem’s president. “With the economy and political climate remaining paramount concerns, there is little to suggest that either millionaires or the affluent will grow terribly excited about investing anytime soon.”

In response to an open-ended question about the most serious threat to achieving their financial goals, affluent investors in March cited: the economy (26%); the political climate (25%); unemployment (12%); health-related issues (6%); market conditions (4%) and inflation (2%). Those choosing the economy rose from 18% in December 2009, the last time this question was asked, and those citing the political climate rose from 22%.

Millionaires expressed slightly more concern than the affluent about both the economy (28%) and the political climate (27%).

The Spectrem Affluent Investor Confidence Index is based on 250 monthly interviews with the financial decision-makers in households with $500,000 or more in investable assets. The Millionaire Index is based on a subset of the overall group.

The number of U.S. households with a net worth of $1 million or more increased 16% to 7.8 million last year, according to Spectrem. The increase last year follows a 27% decline in millionaires from 2007 to 2008. (