Czechoslovakia has all of the markers for a popular philatelic country. It has a highly educated population. As a central European country, its population shares many characteristics with the Austrians, Swiss, and Germans- all of whom are avid collectors. Since the downfall of communism and the introduction of the free market, Czechoslovakia should be an active collectors market with increasing stamp prices. But the popularity of Czechoslovakia has never been as great as outsiders imagine that it should. The reason probably is that the many nationalities that were united to form Czechoslovakia never warmed to the stamps of their pieced together nation and are more attracted to the stamps of the component states with which they are more associated. And second, the vast number of Czechoslovakian stamps are daunting to anyone wishing to collect them. This is true of all of the former communist block countries. The many thousands of stamps issued since WWII makes for lower collector interest. Most people looking for what to collect want a hobby not a life's work, and though the advanced philately bug is catching, few want to be infected right away.
There is one early Czechoslovakian set, though, that has appeal on many levels and could perform well in the years ahead. It is the 1934 Czechoslovakia Music sheet. Music thematics have long been among the most popular in philately and this sheet is one of earliest world wide issued devoted to music and may be the first with musical notation on it. The set is scarce in its own right. When you factor in that the stamps of Czechoslovakia should be better in general than they are and that this sheet is one of the premier items of a popular thematic, the possibility of price increases for these sheets is a good one. If you can find a nice set for a couple of hundred dollars you should think about getting it. And the set was issued without gum so your long term storage issues are easier too.