In Thailand, I've only been to Bangkok and I think a couple of days is enough for the city. I've done two trips to China, each was 5 weeks. You can spend a long time in Beijing, certainly. Maybe add Xian to the China trip? It's not a day excursion, but if you spend some time in the city, you can see more than the terra cotta warriors. There is a mosque. (Xian was one of the furtherest stops on the Silk Road.) If you want to see a very different side of China, then Kasgar (Kashi) would be interesting, or perhaps a day a Lhasa.