A surging stock market is fostering a renewed sense of optimism among those whose fortunes are most closely tied to the equity market-millionaires and ultra-high-net-worth individuals with over $5 million in investable assets.

But mass affluent investors with between $100,000 and $1 million remain challenged and concerned by the current economic environment, according to Spectrem Group.

This divergence among the different wealth segments of the U.S. population shouldn't be too surprising. After all, falling home prices and rising food and energy costs exact a much greater influence on the lifestyle of the mass affluent than they do on millionaires and multi-millionaires, Spectrem president George Walper told attendees at the Innovation and Growth Forum in Chicago on Wednesday.

It's not that millionaires and multi-millionaires are oblivious to the problems of the middle-class. All three groups are expressing less optimism than they did two months ago.

But the national debt has replaced a prolonged economic downturn as the chief concern of both the wealthy and ultra-wealthy, with 76% and 81%, respectively, citing it as a major concern. Among the mass affluent, 74% say a prolonged downturn remains their major concern. All three groups worry about higher taxes as well.

Having enough money set aside for retirement is a serious concern for 63% of the mass affluent, but only 46% of the affluent and 31% of the ultra-high-net-worth folks worry about it