Testing cleanup filters with VirtualDub to upscale the image from letterbox to anamorphic I remembered I'd downloaded a filter a long time ago that does a 2x resize but with edge detected interpolation, from what I can tell it doubles the image size without increasing grain, this is an example of scaling a crappy mpeg1 frame compared to Lanczos3:
How I use it is to crop the 4:3 source so I just end up with the letterbox image, 2x resize with the edgeresample filter, rescale it again but with Lanczos3 to 1280x545 to get 1:1 aspect ratio image, apply a sharpen filter and then finally Lanczos3 resize & add black borders to get an anamorphic PAL image.
Slow, yes, worth it, definitely. If anyone wants the VirtualDub filter it it's available here: edgeresample.zip (it's not optimised so expect long filter times)