The way things appear to be changing cashback cards might be best if you do not plan on traveling for five years. Save the money you get in cashback in a separate account for travel. Then maybe six months out from your travel date you can look at the world as it exists at that point in time and you and your spouse can apply for a bunch of cards for whatever bonuses are available then that will help you out on your trip.

Another thing you could do is app-o-rama for cards that have points that can be converted easily to cash. So cards like Chase cards that give Ultimate Reward bonuses have a minimum cash value, you can get those and if things don't look good for saving points you can cash them out.