Increased interest in these high-end investments has helped raise their value recently. Record auction prices haven't hurt.
Collectibles can help diversify a portfolio
"Prices of luxury items, such as classic cars, ancient Chinese ceramic art, and rare coins, have reached record amounts in recent years. Such items can be a good way for wealthy investors to diversify their long-term investment portfolios."
" The considerable returns of rare stamps and coins -- 255 percent and 225 percent, respectively -- would also pique investors' interests."