dinbangkok. I called TG Gold office just a moment a go. They confirmed that any economy ticket (except V/W) can be upgraded to biz (and bypass premium economy in doing so). I asked explicitly about the JKF-BKK service and got the same answer. This is consistent with the information in the Gold Upgrade welcome letter.
Upgrading from miles alone is different - the TG site has the info.
http://www.thaiair.com/images/Royal_...w29_Dec_05.jpg
Basically, the upgrades are by one-way sector (can be a planning trap to think they are return) as follows:
BKK-JFK/LAX (or vv)
Econ (Y/B/M) to Biz 40,000
Econ (all except V/W) to Biz 50,000
Econ (all except V/W to Prem Econ 35,000
Prem Econ to Biz 35,000
Biz to First 60,000 (note no F on non-stop flights)
TiteG4. That appears to be the experience of many TG ROP Gold members. It is doubtful that it is an explicit benefit. One exception, however, seems to be if buying an upgrade from Y/B/M to C it is immediately confirmed per TG's website:
Upgrades from Economy Class booked as Y/B/M are reduced by 20% with upgrading automatically to Royal Silk Class.
I intend to do this with the family on our return from NZ in Jul.