I use a Nikon Coolsan III and on its own Kodachrome looks awful. So I bought Vuescan and it changed my life, well, not quite but it meant I was able to submit my old shots with confindence.
Once scanned in Vuescan, I crop and level the image and then clean it up in Photoshop 7. To do this, I magnify the image on the 200% setting so I can I identify all the grime (of course, I have used a soft opticians cloth carefully and a blower already). Once cleaned with the cloning tool, I rename file as (say) "G-BNLX_clean.tif". The I shrink it to 1024 across and precede to apply Unsharp Mask using Amount=70, Radius=1, Threshold=0 and then re-save as "G-BNLX_anet.tif", and then again as a jpg file on maximum quality setting 12.
Sometimes, I need to lighten the image and try to make a note of this in the filename in case I need to re-do.
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Photo © Ray Pettit
I don't know if this is perfect as most of my uploads are oldies where the screeners give more tolerance, despite those great shots by Johan and Tim's father Peter.