I guess it depends on the demand. When I think about it, a 25GB torrent is HUGE. What do you do with so many images? You'd probably need to go through them and pick the ones you like (either that, or set them all as random wallpapers and just cycle until you find something you like).

Part of me thinks that it'd be more manageable to get smaller torrents, but that's highly dependent on how exactly these torrents are used.

Personally speaking, updating yearly is not an issue... I have SO MANY IMAGES to go through from the 2011 pack, that by the time I am finished, the year 2012 will be done already :B But I guess people asking for more frequent updates have a different way of using the content...?