Better vertical space between paragraphs and centered tabular or figure

Define your own environment:

\documentclass{article}
\usepackage[margin=2cm]{geometry}
\usepackage{booktabs}
\usepackage{mwe}
\usepackage{lipsum}

\newenvironment{rcenter}
 {\setlength{\topsep}{.5ex}\center}
 {\endcenter}

\begin{document}

\lipsum[2]
\begin{rcenter}
\begin{tabular}{ccc}
\toprule
a & b & c\\
\midrule
1 & 2 & 3\\
4 & 5 & 6\\
\bottomrule
\end{tabular}
\end{rcenter}
\lipsum[2]
\begin{center}
\begin{tabular}{ccc}
\toprule
a & b & c\\
\midrule
1 & 2 & 3\\
4 & 5 & 6\\
\bottomrule
\end{tabular}
\end{center}

\lipsum[2]
\begin{rcenter}
\includegraphics[width=.75\linewidth]{example-image}
\end{rcenter}

\lipsum[2]

\end{document}