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As a reader, it doesn't add much, if anything.  Note that all the same meaning is still conveyed in your examples when "after all" is removed.

It's one of those content-free words or phrases people say, but that don't really mean anything.  When used sparingly and in the right context, it can give an additional emotional feel, but that's about it.

The reason you can't seem to find a replacement is that the original has no real meaning in the first place.  Anything you try to replace it with does have some meaning, altering what is said at least a bit.

It's just fluff, after all.