During World War II, the Polish Government in Exile, based in London, issued stamps for letters posted from Polish merchant ships and warships. In June of 1944, it issued a set of four stamps honoring the final capture of Monte Cassino by Polish forces (Scott #3K17-20). The Battle of Monte Cassino was actually a series of four costly battles fought by Allied forces (from many different nations) so that they might seize Rome. The pivotal role played by the Poles in the final fourth battle against the Nazis gave hope to those fighting for Polish Independence. Only 55,000 sets were issued, and Scott '10 values it at $ 30.00 for unused ($70.- for NH), and $ 80.00 for used. Philatelic covers bearing the whole set exist, and these are quite desirable.
The set has dual appeal to collectors of Poland and World War II topicals. I have little information regarding demand for the set in Italy, but there is a potential for that to become significant, as well.
With 38 million people, Poland is one of the fastest growing economies of all of the formerly Communist countries, with annual GDP growth averaging about 5.5% over the past 5 years. The nation has steadfastly pursued a policy of liberalizing the economy, and was not severely impacted by the recent global financial crisis. It is likely that Poland will be one of the world's fastest growing economies over the next several decades.
Better stamps of Poland should rise in value as the country prospers and the population of Polish stamp collectors increases. Interest in Polish history and national pride are important elements in the culture of this oft-conquered people, and there are some 10 million Polish-Americans with ties to the country.