(Forbes) - Next time you feel hard pressed to justify that expensive hobby of yours, consider this: more and more of America’s most affluent investors are taking up so-called “hobby investing,” and often making good money in the process.

The premise of hobby investing is simple: you invest in products you would have bought for fun anyways, such as art, wine, stamps, classic cars and more. Not only can this approach add tremendous diversity to a portfolio, it can also produce some robust returns. As richly priced stocks, poorly yielding bonds and fears of inflation make tangible assets more appealing to investors, more than half of high net worth Americans are adding hobby investments to portfolios, according to BMO Private Bank.

Many investors don’t expect to make a killing. About 62 percent of hobby investors are doing so mainly for fun, according to the study. About 40 percent also look forward to passing something unique down to heirs, the study said. For investors like this, the goal is less about making competitive returns than finding a weekend activity that pays for itself, said Jack Ablin, chief investment officer of BMO Private Bank.

For the 39 percent who are looking for a sound investment, however, a pretty strong case can be made for hobby investing. If you pretend for a moment that a car or a bottle of wine is a financial instrument, you might notice that it has some pretty appealing features. One of the most compelling is diversification. Wine, for example, has only a 15 percent correlation with the market, said Mark Ricardo, president of Trellis Fine Wine Investments. Correlations are similarly small for antique cars, as well as most fine art, experts say. When the financial crisis struck, many of these assets took a smaller dip than the S&P 500, and then recovered more quickly.