I think you’re right. It is likely not enough benefit for the extra work. With that in mind, I’ll go back to just uploading the “final” image and wait for CAA to process the thumbnail images whenever it happens. If people are interested, they can always view / download the original uploaded image.
That’s the standard size for album cover art uploaded to Fanart.tv, so I’m generally creating JPG files that resolution to upload there anyway.
There has been an ongoing discussion in Advice on Scanning Cover Art that seems to be advocating much higher resolutions and (preferably) PNG files for the archival images on CAA. The (unofficial) MB guideline indicating scan resolution of 300 dpi is being challenged, and there are a lot of conflicting opinions and advice. I have to admit, I’m beginning to find it all a bit tiresome. 