Are you familiar with Ita Software by Google? It is a tool that allows undecided people like us to enter several departure and destination cities; and find the cheapest flight for a given period of time.
Example: I’m looking to go to America from Europe, I put all “nearby” CDG and “nearby” New York airports. For “nearby” you can select the airports yourself or add all those that are within 25/50/75/100… miles.
It’s really interesting, by doing several simulations, we found for example that it was cheaper to do Sydney – Honolulu (stopover 7 days) – Los Angeles (581€) than to do Sydney – Los Angeles (746€).
Here is a small screenshot to show you how I make my itinerary for the 2nd round-the-world trip and decide whether or not I take dry flights or the round-the-world ticket (click on the image to zoom)