How to make the vertical rubber space between paragraphs as compact as possible?

Question

I am setting a document in 2 columns via the multicol-package. It is a newspaper-like document.

How can I force LaTeX to–ideally–remove as much extra-added vertical rubber space, which is used to make "consistent" looking line breaks and vertical spacing between paragraphs on one page?

All the while that spacing might look alright and good for that one section, it seems to be noticeably different in other sections. This is somewhat... meh. Not the best look, honestly.

So far I only found this code:

\everypar=\expandafter{\the\everypar\loosness=-1}
\linepenalty=1000

(Note: I am aware that it is literally impossible sometimes unless I were to use floats, but they are super tricky–if not impossible–to use in multicol-environments... I think (based on reading threads right here on TeX.sx. So I would just like to try something else regardless.)

MWE

\documentclass[
11pt,
a4paper,
false-,
]
{scrartcl}
\usepackage{
lmodern,
multicol,
blindtext,
mdframed,
}
\usepackage[svgnames]{xcolor}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\listfiles
\begin{document}
\begin{center}\huge
Title stuff
\end{center}
\begin{multicols*}{2}
\section{Word}
There really are some words.
And then some.
AAaaaa bbbb cccc.
Now here is something interesting: {asdf}.
\blindtext[1]
\begin{center}
\rule{\columnwidth}{10pt}
\end{center}
Some words to form a sentence.
There really are some words.
And then some.
%\addvspace{2ex}%
There really are some words.
And then some.
\begin{center}\color{DarkBlue}
\rule{\columnwidth}{10pt}
\end{center}
\blindtext[1]
\everypar=\expandafter{\the\everypar\loosness=-1}
\linepenalty=1000
\begin{center}
\fbox{
\begin{minipage}[t]{0.5\columnwidth}
1 - Some stuff.
Words and such.
There really are some words.
And then some.
There really are some words.
And then some.
\end{minipage}
}
\end{center}
\blindtext[1]
\begin{center}
\fbox{
\begin{minipage}[t]{0.5\columnwidth}
2 - Some stuff.
Words and such.
%There really are some words.
%And then some.
There really are some words.
And then some.
\end{minipage}
}
\end{center}
\blindtext[1]
\end{multicols*}
\end{document}

Screenshots of MWE

Answer 1

As far as I can tell you are mainly asking about space above and below center which is \partopsep if it is between paragraphs or \topsep otherwise. Setting this to 0pt produces

\documentclass[
11pt,
a4paper,
%%%% ? false-,
]
{scrartcl}
\setlength\partopsep{0pt}
\setlength\topsep{0pt}
\usepackage{
lmodern,
multicol,
blindtext,
mdframed,
}
\usepackage[svgnames]{xcolor}
\usepackage[T1]{fontenc}
% not needed unless your latex is old \usepackage[utf8]{inputenc}
\listfiles
\begin{document}
\begin{center}\huge
Title stuff
\end{center}
\begin{multicols*}{2}
\section{Word}
There really are some words.
And then some.
AAaaaa bbbb cccc.
Now here is something interesting: {asdf}.
\blindtext[1]
\begin{center}
\rule{\columnwidth}{10pt}
\end{center}
Some words to form a sentence.
There really are some words.
And then some.
%\addvspace{2ex}%
There really are some words.
And then some.
\begin{center}\color{DarkBlue}
\rule{\columnwidth}{10pt}
\end{center}
\blindtext[1]
% commented out as it is too weird
%\everypar=\expandafter{\the\everypar\loosness=-1}
%\linepenalty=1000
\begin{center}
\fbox{
\begin{minipage}[t]{0.5\columnwidth}
1 - Some stuff.
Words and such.
There really are some words.
And then some.
There really are some words.
And then some.
\end{minipage}
}
\end{center}
\blindtext[1]
\begin{center}
\fbox{
\begin{minipage}[t]{0.5\columnwidth}
2 - Some stuff.
Words and such.
%There really are some words.
%And then some.
There really are some words.
And then some.
\end{minipage}
}
\end{center}
\blindtext[1]
\end{multicols*}
\end{document}