The degree of difficulty of a philatelic specialty is determined by three components. First is the intrinsic scarcity of the material, second the cost involved, and third the number of specialized striations into which the field has been separated. Scarcity and cost are related. Scarcity is an intrinsic value related to the amount of material that is available to collectors. It is derived from the numbers that were printed and more importantly the numbers that were saved and have been passed down to stamp collectors. Cost relates to how that intrinsic scarcity interacts with demand. Honduras has many very rare stamps that sell for only a few dollars. Great Britain have many relatively common stamps (such as the Penny Black) that sell for a hundred dollars or more. So cost and scarcity are different factors when considering a specialty. Most want scarcity; not everyone wants costly. And third, the degree of specialization needs to be considered. Each philatelic specialty has a tradition of how in depth it is specialized in. Areas like Germany have literally millions of recognized stamp varieties in the Michel specialized catalog. Areas such as Russia are far less specialized and let the collector concentrate more on getting the basic stamps.
Greece
By these criteria, Greece rates well as a specialty. Most of the classic stamps are quite scarce and difficult to find. But because Greece is not a major philatelic area and has a small national market and has experienced economic difficulties lately, even rarer Greek stamps are quite affordable. As far as the degree of specialization is concerned, Greece is a serious philatelists delight. Even seasoned specialists argue long into the night over basic catalog number classifications of the classic Hermes Heads. (actually Greek philately, Canal Zone and several others areas have always attracted the more disputatious collectors for reasons which I will try to develop in another article). There are hundreds of modestly priced Scott listed varieties and the Occupation issues, and the extensive Greek area material such as Crete and Thrace make this one of the more popular areas for collectors who want lots of philatelic fun and sense of accomplishment for not an enormous outlay.