I guess I accept that some people like to try new experiences, but I don't get why, unless time is of great importance, one would take a train to SGS.

I have travelled this route (Suvarnabhumi-SGS) about 30 times. I have driven myself, taken taxis and hotel limo. In light traffic, it's 30 mins. In the worst traffic, it took 90 mins. Regardless of time, it was in the comfort of my own seat of an a/c vehicle and I didn't need to touch my luggage. Surely cost isn't the determining factor for someone prepared to spend 4500-7500THB on a hotel. Sorry to be off-topic.