In 1955, the United Nations celebrated its 10th Anniversary, and many nations issued stamps and souvenir sheets commemorating the event. South Korea issued a set of two stamps (Scott #221-22), which are relatively common, but it also issued a set of two presentation sheets (Scott #222Note), of which only 1,000 were issued. Many stamps of South Korea from the '50s were issued along with these accompanying presentation sheets, which were given to dignitaries. Scott does not recognize most of them, but they are listed in Michel and in the Korean Postage Stamp Catalog, which prices them at 960,000 won, or about $850.-.
Because they are usually not listed by Scott, Korean presentation sheets, of which a 300 to 1,000 were produced, can often be bought at U.S. auctions for 25% - 35% of their Michel or KPSC values. Whether or not they remain at low levels will depend upon whether they are widely accepted by Korean collectors. In the meantime, I believe that the most prudent strategy for speculating on them would be to focus on those feature popular topics, such as the U.N..
I continue to like the U.N. as a topic, long-term. The market for U.N.-related topicals should grow over the very long haul as institutions of world government develop in order to take on serious (and possibly existential) problems which can only be coped with globally. Despite the present inadequacy, corruption, and ineffectiveness of the U.N., I view its reform and gradual strengthening as a gradual but irresistible trend.
South Korea, a nation of about 50 million people, is one of the fastest growing economies in the world. Currently, it is the world's 13th largest economy and eighth largest exporter. It's export-fueled economic growth has led to a miraculous explosion in its GDP, from almost nothing 50 years ago to about $1 trillion today. Annual GDP growth has averaged 4.2% over the last 5 years, reflecting a slowdown in 2009 due to the global financial crisis. Furthermore, South Korea may be the most rapidly aging nation on earth, as its 65+ population is expected to more than quadruple from 9% in 2005 to 38% in 2050. Obviously, this could pose economic challenges for the country, but it will almost certainly add to its stamp collecting population.