I've said it once, and I'll say it again: the fundamental theorem of backups is:
Backups != Archives
When you create a backup (as opposed to an archive), do not rely on the backup to hold files you don't currently need. If you do, you'll amass several "backups" that you can't get rid of because they contain files you might need. Instead, put files you're tired of looking at in an *archive*.
This definition of "backup" implies that it is almost completely safe to destroy an old backup to make room for a new one. Or, better yet:
(cd "$HOME"; rsync -av --exclude-from="$HOME/list-of-huge-files" "$HOME" "/media/backup-disk/homedir")