Just got a 47inch smart LG TV, using True Visions satellite, the HD channels look great but the wife is complaining that Thai Channel 3 is crap picture quality with this big screen (and she's right). I would have thought True would have prioritised satellite bandwidth for the most watch channel in Thailand (Ch.3). Any workarounds for good quality Thai Ch.3 TV on a large screen (IPTV, etc.)?

I've got the same set up as you but with a 55 in TV. The thai channels look OK to me for SD, obviously they are not going to look as good as the HD channels.

I have a amplifier that also can upscale and assist the picture quality. That helps somewhat.

SD channels will never look as good as HD, even when passed through a box that upscales!!

My satellite receiver upscales all channels to 1080, with a little improvement, but not a lot.

As we say in the computer industry in Garbage in, Garbage out

Until the Thai channels bite the bullet and improve their broadcast quality, you will not see a benefit.