Although the costs associated with Korean unification will be unmatched in modern times, the potential benefits that could be achieved by a unified Korean state would almost surely outweigh the costs over time. In a 2009 analysis by Goldman Sachs, its authors stated that a unified Korea had the potential to overtake Japan and Germany's GDP's within 30-40 years. This statement is plausible due to certain benefits that North Korea would bring to a unified Korea, although it would be decades before the benefits would be fully realized.
Even though South Korea would be integrating nearly 23 million North Koreans who would need large amounts of medical and economic assistance, it would be inheriting a relatively young population, something that would aid in offsetting the South aging population, as well having one of the lowest reproductive rates in the world. The North Korean population is also relatively well-educated for a country of its current condition, and many of its citizens could contribute relatively quickly within an integrated economy. In terms of size, the territory of a unified Korea would nearly double, and within this land lays a windfall of mineral wealth that could indeed vault Korea past Japan and Germany within 40 years.
There have been estimated of mineral wealth inside North Korea to be of an estimated $6 trillion USD. Much of this wealth is in the form of rare earth goods that are used in the production of hi-tech goods: a South Korean specialty. The ability for Korea to have these minerals within their borders, as well as potentially moving production factories from China into former North Korean territory where abundant reliable and cheap labor could be found, would accelerate the Korean economy.