Would you have paid $18K to fly to Japan though? The "cents per mile" is high but it's better to measure your WTP (willingness to pay).

BTW, you can regularly get west coast to Japan in business class for ~$3-4k/pp. ex. https://goo.gl/flights/BDTu. If you wait for deals, there was Vancouver - Japan/Hong Kong/SE Asia for ~$2k in business class for a while. Business class prices have been consistently dropping transatlantic (TATL) and we're seeing that transpacific (TPAC) too, albeit more slowly.

I think what you did was smart, but there's really no way to continue to get that kind of value from your miles. You could get the other Amex cards (~150k MR?), and other Chase cards (~150k UR?), but hard to repeatedly get big bonuses like that :P

Totally agree though that keeping one or both of those cards is great for the right kind of spend. It's just not like a free trip to Europe every quarter like it used to be.