biblatex: How to show individual bibliography entries as footnote?

Question

Using a BibLaTeX (+ Biber) bibliography, I want some particularly important entries to also show up as footnotes on the page they are cited. Actually, it's about a Beamer presentation, but my question is mainly concerning the bibliography entry, so let's keep it simple. The footnote should look like the regular bibliography entry and the approach should work with any citation style, not just numerical ones. \footcite doesn't fit these requirements and neither does this older question.

The following code achieves this, in principle. (The \vspace is just to make the following picture more compact.)

\documentclass{article}
\usepackage[style=alphabetic]{biblatex}
\bibliography{biblatex-examples}

\newcommand*\citeWithEntry[1]{%
  \begingroup%
  \renewcommand\thefootnote{}%
  \cite{#1}\footnote{\cite{#1}~\fullcite{#1}}%
  \addtocounter{footnote}{-1}%
  \endgroup%
}%

\begin{document}
\vspace*{\fill}
Some text with an important reference~\citeWithEntry{hammond}.
And then, we have the same citation again~\citeWithEntry{hammond}.
\end{document}

My questions:

• Are there any side effects of using \cite twice here or is there any other way to print the citation label?
• How can I avoid printing the same entry multiple times when one reference appears more than once?
• Is there any more “idiomatic” solution with biblatex?
• Bonus: Can I achieve this effect without a dedicated command? For example, BibLaTeX supports categories and keywords. Can I automatically generate this footnote bibliography entry for any \cite that refers to an entry with a specific keyword or category?

Answer 1

Combining the two variants of this answer, which my previous searches did not find, I can solve all but the bonus question:

\documentclass{article}
\usepackage[style=alphabetic,citetracker=strict]{biblatex}
\bibliography{biblatex-examples}

\makeatletter
\newrobustcmd{\mkbibblfootnote}[1]{%
  \iftoggle{blx@footnote}{%
    \blx@warning{Nested notes}%
    \addspace\mkbibparens{#1}%
  }
  {%
    \unspace
    \ifnum\blx@notetype=\tw@
      \expandafter\@firstoftwo
    \else
      \expandafter\@secondoftwo
    \fi
    {\csuse{blx@theendnote}{\protecting{\blxmkbibnote{end}{#1}}}}
    {\csuse{blfootnote}{\protecting{\blxmkbibnote{foot}{#1}}}}
  }%
}
\makeatother

\newcommand\blfootnote[1]{\begingroup\let\thefootnote\relax\footnotetext{#1}\endgroup}

\DeclareCiteCommand{\citeWithEntry}
  {\usebibmacro{prenote}}
  {%
    \mkbibbrackets{\usebibmacro{cite}}%
    \ifciteseen{}{%
      \mkbibblfootnote{%
        \mkbibbrackets{\usebibmacro{cite}}%
        \setunit{\addspace}%
        \usedriver
          {\DeclareNameAlias{sortname}{default}}
          {\thefield{entrytype}}%
      }%
    }%
  }
  {\multicitedelim}
  {\usebibmacro{postnote}}

\newbibmacro*{morecite}{%
  \printnames{labelname}%
  \setunit{\addspace}%
  \printfield[parens]{year}%
  \setunit{\nametitledelim}%
  \printfield[citetitle]{labeltitle}}


\begin{document}
\vspace*{\fill}
Some text with an important reference~\citeWithEntry{hammond}.
And then, we have the same citation again~\citeWithEntry{hammond}.
\end{document}