In their efforts to be everything to everyone, America’s megabanks are in danger of becoming a lot of nothing to nobody, especially when it comes to members of the “mass affluent” market, a new study shows.

The rapidly growing number of Americans with between $100,000 and $1 million in liquid assets generally think they are poorly served by the three or four financial services with which they now do business, the study by Guideline says. The research company’s work indicates that the investment firms that market solid, personalized service will be the ones left standing after a shakeout in the crowded financial services field during the coming decade.

“Our most shocking finding is the degree to which the mass affluent feel underserved today,” the managing director of Guideline, Brian Methvin, told an audience of 350 investment advisers in Midtown yesterday. He noted that women, ethnic minorities, and owners of small businesses in this wealth class are particularly neglected by many financial planning firms.

Another finding of the study: Customers are overwhelmingly loyal to their financial advisers, not their firms, which is prompting banks to assign teams of advisers to each customer so that a defection of one adviser won’t result in a noticeable loss of business.

Mr. Methvin said large banks are not effectively utilizing their many business units. “Many bank divisions operate in silos that rarely communicate with each other,” he said.

One of the panelists who joined Mr. Methvin during the presentation was the managing director and head of advertising at Citigroup Global Wealth Management, Steve Cone, who said he thinks it took his bank too long to develop synergies between business units. Citigroup has plans to place Smith Barney branches in 600 of its bank branches. “It took us a while to figure out it would be a good thing to have investment experts in a commercial bank,” Mr. Cone said.

About half of all mass affluent Americans have taken the time to develop a financial plan for themselves and their families. “One of the reasons so many people don’t come up with a plan is that it’s boring as hell,” Mr. Cone said.

The director of advertising and brand management at BlackRock Financial Management, Chris Poe, said he agreed with the study’s assessment that financial advisers were more important than accountants to wealthy baby boomers. His said his firm, which doesn’t sell products directly to the public, must get financial planners to sign on. “It’s all about the adviser — he has to be the hero,” Mr. Poe said.

The study found that although the majority of the mass affluent are white men in their 60s and 70s, their wives are beginning to make many of the financial planning decisions for them. Women are far more likely to consult investment advisers for advice on their savings, according to the study.

Mass affluent customers prefer mutual funds: More than 90% of this group owns shares in at least one fund, yet only 26% own Treasury bills. Indeed, these investors tend to shy away from debt instruments, with only 29% holding bonds.

“The killer app is mimicking services offered to high net worth clients but at a lower price point,” the principal and head of retail marketing at Vanguard, Kevin Feldman, said during the panel discussion.

Mr. Poe of BlackRock said that as banks have merged with other financial services firms, they face challenges in integrating the two: “It didn’t mean anything because most banks couldn’t get past their nasty customer service. If you can’t get my checking account right, why should I trust you with my investments?”