Collectibles markets are driven by passion, not rational thought. But the aircraft-collecting market has seen a split in recent years between those who purchase and restore for love and history and those who are new collectors with an interest in return on investment.

The owners of Redondo Beach, Caliornia.-based Platinum Fighter Sales claim to have brokered more than $300 million in classic aircraft and warbirds (aka military planes) to both types of buyers over the past three decades.

In the last few years, Simon Brown, co-owner of Platinum, has noticed an influx of investors. These clients may not even know what kind of plane they're buying, but they know a good return on investment when they see it.