I never sweat seat assignments on trains, and have yet to end up in less than optimal seats, so I simply don't stress this at all any more.

Regarding your 9C flight, if your fare was on par with other airlines' business class, the upcharge for Spring Plus shouldn't be more than $20 or so, and is well worth it. Since I try my best to avoid eating food on Chinese airlines, Spring's lack of (free) food is actually a plus for me (i.e. fewer bad smells).