When you go to any car show or auction, cars that are gorgeous and have lots of horsepower attract the most attention. The rare ones get even more notice, and in most cases this all translates into greater market value.
All the horsepower in the world won't make a car worth seven figures if it is aesthetically challenged and built in large numbers. And let's face it: We'd all rather be surrounded by things of beauty. I am not talking about wives, girlfriends and children here.
First impressions count for a lot, particularly with cars. A sleek and well-detailed nose is a great place to start. Three examples that come to mind are a Series 1 E-Type Jaguar, 1963 Chevrolet Corvette Sting Ray or a 1940 Ford. Those pleasing front views invite the eye to look further. A Chrysler Airflow or an Edsel is much more polarizing and likely to have as many detractors as fans, despite their many other merits. So beauty really does sell.
As you move on from the nose, flow is important. Both the E-Type and the Sting Ray have incredibly sleek lines that move organically from the nose to the flank, to the haunches and on to the tail. They are considered styling masterworks, and the original, purest iterations are the ones in demand. I would argue that the closed versions of both are the most visually successful.
(Read More: Best Convertibles of All-Time)
Yet, with very few exceptions, the convertibles of these iconic cars carry a significantly higher value in the market because, as they say, "When the top goes down, the price goes up."
Of course, some coupes are so gorgeous that they negate the appeal of a convertible, and the Lincoln Zephyr three-window coupe is a perfect example of a car where coupe and convertible values are very close.