Every specialty collection runs out of wind. You start with great energy and begin to acquire stamps and covers in your area and sooner or later the amount of time you spend searching increases and the amount of money that you need to spend for each item increases. Most collectors get to the point where they are spending more and enjoying it less. This the point where many collectors put their albums on the shelf.
What attracts a collector to one specialty is easily transferable to another, especially if a little planning is done. Certain countries and areas lead easily to each other not only because of historical association and geographic proximity but because of a similar philatelic feel. Most collectors of British West Indies collect all of the islands. Danish collectors often add Norway and Denmark. Not only is there geographic and historical proximity between these areas but the stamps are similar in artistic feel and production values (in the case of the British West Indies they are printed by the same designers and printers).
Of particular interest to many United States collectors are the stamps of Canada. Almost a philatelic little brother, the stamps of Canada after the first few issues are similar in style and feel to US stamps. Canada is very affordable. Except for a few early rarities the entire country can be completed for a couple thousand dollars. And the stamps are well designed, the literature is in English and there are good stocks of most of the stamps in dealers hands which means that you don’t have to spend all of your time looking. If you’ve reached the end of your US rope, Canada is a good country to collect.