I got the same two upgrade vouchers after a not too great experience of having a flight cancelled and then bags lost (and yes, this odyssey also started in BKK). Seems to be the standard compensation when CX is admitting that they really did make a mistake. I've had a few other problems in the past, but normally just get a sorry letter. I don't know of anybody who has gotten more than a couple of upgrade vouchers from CX-- suspect they'll take a fairly hard line on this issue, as they are afraid of setting precedents.