I have to put this post in it because it is also related to the actual topic:
Many of the island territories in the Central Pacific which Japan and the US fought to control were little more than coral atolls, volcanic formations or overgrown sandheaps, many of them small in size and some of them barely above water at high tide. They had few (or no) natural resources, little (or no) arable land, few (or no) indigenous inhabitants, and no industries; the military bases located there had to be supplied from outside with virtually everything they used. They were for most practical purposes 100% consumers and 0% producers.
The value which these islands had wasn’t as industrial production facilities or as sources of income or of goods or of raw materials. Their value was to serve as airbases (and in the case of suitable anchorages like Truk as naval bases) which allowed the domination of the airspace and ocean around them, and to serve as the jumping-off point from which to capture the next island group down the line. So if the rules provide no incentive to capture and hold these territories, the historically realistic solution isn’t to give them an IPC value. The solution is to create a house rule through which possession of an island gives some sort of bonus to a player who uses the island to attack enemy forces around it or as a springboard for an island-hopping advance.