Ross,
[Ross Marshall] “Surely if I scale my 16:9 footage on a sequence 4:3 this just enlarges the pixels, meaning I will lose resolution?”
Nope!!! Converting 4×3 to 16×9 enlarges the pixels, going in the other direction involves either cropping or panning and scanning a selected portion of the image. Try your dropping your nested into a 4×3 timneline and see what happens.
DRW