As it turns out, that vintage Porsche you have your eye on, might actually have a place in your wealth portfolio. Many so-called passion investments, from classic cars to coins to cases of Bordeaux, have handily outperformed the Dow Jones Industrial Average over the last decade as well as the London luxury real estate market, according to the 2014 Knight Frank Luxury Investment Index.

The value of the index, distributed by the London luxury real estate consultancy, shows a portfolio of nine types of collectables, rose by a modest 6% over the 12 months ending June 2014. However, over five years, the index – boosted by big gains in rare coins and classic cars – has grown 44%. Its 10-year performance soared 182%.

But while beautiful objects such as fine art, antique jewelry and stamps might be desirable to buy and enjoyable to own, they can be even more volatile than the market, with their fortunes falling as fashion and tastes change. Antique furniture values, for example, have slid dramatically over the last 10 years, with the exception of early and mid-20th century pieces, according to data collected by Knight Frank. Fine wine also has had a bumpy short-term ride in recent years.

And getting out isn’t always easy. Markets for these items are often less liquid and carry higher dealing costs than stocks. At auction, buyers can usually expect a 15% to 25% premium on the goods they acquire, with a similar fee for sellers.

So what should you keep in mind if you want to start collecting?

• First, you’ll need to do a huge amount of research. This includes pinpointing major buyers, marketplaces, auctions and other events, as well as very specific asset performance information and exit strategies.
• Choose investments that have a large collecting community. Is this community growing or shrinking?
• Think long term. You must be willing to enjoy the ride, and it could be bumpy one.
• Put passion first. Because you will be spending a lot of time studying it, make sure it gives you real pleasure. 
• Take your time. One of the most common mistakes is buying too much too fast, and winding up with mediocre pieces.
• Focus on the truly rare. Look for unique, less mass-produced items that will hold their value better.

Remember that the key word in the phrase “investments of passion,” is “passion.” You should buy things only because you truly love them.