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This story is part of Money magazine's story 5 retirement choices: Get 'em right, live well which covers big decisions that can dramatically boost your income in retirement.

Once you determine how much of a saver you are, you have several more decisions to make -- including how you invest your portfolio.

Decision No. 2: How should you divide up your money?

The decision: Once you've amassed a portfolio worth more than five figures, you may wonder whether you should branch out from plain-vanilla stock and bond funds.

To hear some advisers tell it, you can't have a truly diversified portfolio unless you spread your money among virtually every asset class, sector, and subsector under the sun: hedge funds, currency, single-country funds, precious metals, exotic ETFs.

Why it's important: You can capture more than enough of the benefits of diversification -- solid returns while minimizing risk -- with a relatively simple stocks/bonds mix.

Related: Betting your retirement on stocks

Start by making sure you own a broad swath of U.S. stocks and bonds. Then add developed and emerging foreign markets.

For inflation protection, you might pick up some real estate and TIPS. Adding more to this basic blend isn't likely to appreciably boost your performance.

In fact, stocking up on a dozen or more different assets may work against you. One reason is the phenomenon that asset-allocation expert William Bernstein refers to as "overgrazing" -- as more and more investors plow money into a newly discovered alternative investment, the lower its expected return.

Related: Investing in TIPS - Can retirees beat inflation?

"The first ones in get sirloin, but the latecomers get hamburger or worse," says Bernstein. Many nontraditional assets also come with hefty fees.

As you pile on more investments, monitoring and managing them become harder.

"If you've got upwards of 20 different investments in 401(k)s, IRAs, and taxable accounts, you're talking about a blizzard of trading every time you rebalance," says Wealthcare Capital Management CEO David Loeper.

Best move: The simplest way to create this mix is by using index funds or ETFs from our Money 50 list. Aside from simplicity, they have the advantage of certainty: These funds strictly follow defined benchmarks, so you know exactly how they'll invest.

Most important, though, resist the urge to jump onto the alternative investments bandwagon. Says Bernstein: "Wall Street needs to sell them, but you don't need to buy them."