I think I have to agree with you on your first point. Personally I speak Dutch and English (and a little bit of German and French, as every Dutchman), but I feel differences between Dutch, English and German, even though all three of them are Germanic languages (yes, I left French out) English is more polite (at least British English is) than Dutch and German is harsher. I know for a fact that my nephew, who lives in Germany, sounds completely different when he speaks German, even if he is saying the exact same thing.

As for the second point, words like uhm and like are present in pretty much every language, but I personally don't find that they improve the conversation, they only hamper it. These words are mostly used if you do not know what you want to say or when you do not know which word you need. I agree that these "anchor expressions" are present, but I disagree with your speculation that they would increase the fluidity of the conversation.

What I would like to add is that in when you converse in your native language, you use small jokes and wordplays (just pay attention). These small jokes and wordplays lighten up the conversation and make is seem less serious. I think that the absence of these jokes when you speak in another language might also add to the seriousness of the conversation.