Can I ask where do you get your First Class SIA tickets from? Are you getting a round the world ticket?

Many years ago the company I work for used to fly us those Star Alliance flights around the world ticket (3 stops) that's a lot cheaper, but only business class.

For Vietnam depending on the time of the year, Halong bay not bad. The barbershops kind of over rated and your wife not not enjoy that much vs us guys. lol. Also a lot of exotic islands in Vietnam/Thailand/Bali you can go enjoy. You can spend a lot of time in China alone considering you never been there. For natural scenaries China still offer one of the best, especially the mountains. Visa free now if you hold Singapore or Malaysia passport!

Enjoy your retirement trips!!!