We're looking at a cruise out of Tokyo that includes South Korea. Our idea is to spot check cities you probably wouldn't see otherwise and think whether you might return for a longer visit later. We signed up for a cruise in October that is Scotland/Ireland/England in October.
NCL offers air fare for two for only $1,100 (for both), but it's in the back. My wife got exit row seats coming back from Istanbul which helped a lot. And in other news, we're Gold now not that it means much, about to be Platinum.