Are MPEG issues down to signal quality or based around the TV itself.
To be honest I'm not completely sure, I think it's a mixture of the broadcast bitrate and the signal strength as received at your home. The MPEG style artifacts shouldn't be anything to do with the telly unless the digital tunner is just badly designed/cheap, which is unlikely.
I have a sony KD32DX40 in one of the setup menus you can check the signal strength. It may be the same on yours:
Press: i+, setup (blue text button), then go on the menu to >detail setup >system information
This should then show your your signal level, mine is close to high but I still notice artifacts in badly compressed broadcasts.
Then go back a level (blue text button) and make sure software download is set to on. You will then get periodic downloads of the latest software and some fixes.
Watching any DVD and you would think the films are quite old. Monsters Inc or Terminator 3 look as if they are 20 years old. I have tried different scart leads but strangely, I cannot see any difference from the cheap give away to the more expensive ones. Not sure if this means anything
With dvd and tv make sure all picture adjustments (colour/brightness/contrast) are set to default/standard. Sony dvd players have some picture modes wich emulate cinema, "movie1" and "movie2" etc. Some can make the picture look washed out or less briliant.
Is it a fairly decent dvd player, same make/vintage? If its a sony is it set to send RGB to the telly through the correct socket? Are the scart leads fully wired? (The cable will be thick). No strong magnets near the telly or anything etc.
Just some thoughts, I'm not an expert.
cosaw