Plugins vs. Filters Revisited

I know this is a topic that has been discussed a lot previously (e.g. here), but I still feel the topic needs clarification. I’m working on some formal documentation for this topic, so I’d really appreciate thorough and detailed responses.

Firstly, since add_action() and add_filter() are really just referencing the same function (i.e. add_action() is just a wrapper around add_filter() ), doesn’t that mean that *any* time I have used add_action() in my plugins, I could just as easily replace it with add_filter()? I’ve tested this on a few plugins and their functionality seems unaffected. In other words, there is NO difference in execution, it’s merely a mnemonic distinction to give the developer a more memorable function name. Is that fair to say?

The only difference I’m seeing is that hooks designated as “filters” are meant to tie to functions that actually return a value instead of just print it. e.g. consider the following ‘the_content’ hook:

add_filter('the_content','my_function');
function my_function($the_content) {
   return 'I am overwriting all content';
}

This plugin will override the content of all posts on the site. So… given a random hook, how can I tell if WP treats it as an action (where my functions don’t return a value) or if WP treats it like a filter (where my functions *must* return a value)?

Secondly, can anyone provide an example of where add_action() or add_filter() uses the 4th parameter: accepted arguments?

Is there any way to pass additional arguments to a function via the add_action() or add_filter() functions? E.g. imagine a simple function that prints out the time and a string identifier, e.g.
print date() . ' was the time when '. $description . ' happened.';
In such a case it would make sense to use the same function in all hooks, but simply pass a different description. Know what I mean?

Thirdly, are the docs here: https://codex.www.ads-software.com/Plugin_API/Action_Reference and https://codex.www.ads-software.com/Plugin_API/Filter_Reference up to date with WP 3.0?

Thanks for any input!