What if there was a hide button we could use to manually filter out wallpapers we have already seen and decided on whether or not to download/keep/favourite, etc. That way if we sort by 'most popular' or 'most votes' or 'most favourites' or something it won't be mostly stuff that we have already seen.

Hmmm..Unfortunately, the site can't read your mind to know what you've already seen. There is not an individual block for those either.
I think what might be helpful to you is our 'Sort By' feature at the top of the Homepage. Click and a drop box comes down with options. Click Freshness, and you will see all the very latest uploads! These are not in any category or ranking, but just as they are uploaded. You might find a few surprises in there too, until the moderators can 'catch & release' them!

I'm not asking for the site to read my mind. notice i said "Manually". I don't only want to look at the freshest walls. I want to look at the most popular walls, but i don't want to see walls that i've already seen before.
For example let's say a wall pops up which is quite good. let's say it gets 8-10 thumbs up or something. after a few hours, it would probably disappear from the "Freshest" categories, but still not quite be popular to make it into the "most favourites" category.
just chuck in a little box which we can click on to hide wallpapers and add a show/hide chosen walls option in my account settings.