Captain Robert April wrote:
You wouldn't gain anything in image quality.
You would gain in the background painting image quality.
high definition has 10x the color information [and 6x the resolution]. All that extra color information make for more accurate colors and subtle gradations that NTSC/(SMPTE 170M) standard in standard definition cannot show.
The 2-D hand animated cells will have sharper lines as Start Wreck
mentioned and you will see it on "More Tribbles, More Trouble" TAS episode in HD on TOS season 2.
The IGN review I quoted here
brings up the dust issue though that was not removed from the TAS master.