Recently, I compiled a .pdf of a CD booklet and uploaded it on the Cover Art Archive. In the edit notes, someone mentioned something about uploading cover art in .png since it’s lossless, whenever possible. This is something I don’t normally do, except for CD scans, where I delete the white background making the central hole transparent and .png is the most common / popular format that supports transparency. To be honest, I’m someone who loves high quality cover art and from now on I have decided I’m gonna start uploading everything in .png but I’ve also started thinking about re-uploading all my scanned cover art in this format as well. File-wise, it’s not going to be a big trouble, since I have all the raw files and have saved each image as a separate project file, so I can just re-export the stuff in .png in most cases but database-wise I will have to delete the old images and upload the new ones, both of which are going to need voting, which makes me thing it might not be worth the hustle? I mean, .jpg files are totally acceptable and I’m only thinking of doing this for the sake of picture quality, so what do you think I should do?
I upload 600dpi / 85%JPG images @ up to 3.5MB per file. Seems a reasonable size and quality to me.
If I download PNG artwork that is bigger than my music files I tend to convert to JPGs for my own use. I like artwork with my music, but the biggest screen it is on is a 50" TV so I find a 30MB PNG overkill for that.
Others like the extra file size. Better too big than too small. 
Everyone is different.
No one will complain if you swap \ upgrade your artwork. I’ve gone back over some of my earlier uploads that were done on a lower quality scanner. Replacing grey washed out images with more vibrant\real colour versions.
One interesting point of CAA is they will keep both old and new artwork that has been uploaded.
It is the Cover Art Archive. And it’s always best to archive the best possible quality. Anyone who wants lower size/quality can use one of the automagically resized options, or resize/convert to a more appropriate format themselves. And those resized images will be higher quality being sourced from lossless originals.
But as you say, it requires convincing voters and some people might not be convinced. Though I imagine if you explain in your notes that you are the original uploader and that you are uploading lossless copies to replace the lossy ones people would hopefully be receptive to it.
It’s more work, so I won’t tell anyone to do it 
But I definitely am always in favour of highest possible quality being added. I love being able to enjoy the detail in covers. As the name “Cover art” suggests, it’s literally art itself.
Don’t they only keep the thumbnail that is shown in edit history? If you click a removed image it returns 404 in my experience.
Don’t think I have ever seen someone down-vote an art upgrade.
Like you I dislike 600x600 images, or jaggy compression. You still get all the details in a slightly compressed JPG. Storage size is the main reason I don’t bother uploading massive PNGs. Similar to why I don’t scan at 1200dpi.
The automagically resized options on site are a bit out dated as it offers 1200x1200 as highest quality. I always download the original and change things moving to local storage. Bigger the better. I just feel sorry for Picard when it is pulling in a booklet at full PNG resolution at 30MB a page 
Need a bit of patience on those days.
Maybe when I last checked it it was on the same day I had deleted the older artwork. Probably just a slack in the clearout. Can’t remember the details…
Nope. The one in edit history is different but here’s an example:
There are 5 images shown on our side but if you click on the Internet Archive link you can see all 11 - including the removed ones.
I edit and scan with archival in mind (not just reference for credits etc) - if I’m spending hours scanning, I don’t want there to be any chance that someone is going to re-do the work in 10 years. So I think it’s worth it 
I also don’t think you’re going to get any no votes.
The main question is if you think it’s worth it - it’s your valuable time you’ll be spending.