Yes, IME TG domestic J is worth the difference. I like Thai domestic business - priority boarding, a snack/light meal dependent on the time of day, cold (soft only) drinks & tea/coffee, complmentary newspapers. Generally, very attentive service too. The seating is way superior to BA domestic/euro J. I think the worst seat pitch is c38" (equal to BA WT+!") and if you get the right a/c c80" on the B744 (seated in F but paying J, if you check-in early enough). You will get lounge access too, if you don't already have *A Gold. Extra miles too. Enjoy.