Of course you can!
\newcommand{\wrappic}[3][1]{%
\par\noindent\mbox{%
\begin{minipage}{0.3\textwidth}
\includegraphics[scale=#1]{#2}
\end{minipage}%
\begin{minipage}{0.7\textwidth}
#3
\end{minipage}}
\par}
Note that the tabular environment serves no purpose and it also creates an overfull box, because you're not taking into account the intercolumn spaces, so that the sum would be larger than the text width.
Now \wrappic[0.6]{flower.jpg}{this is a rose!} will do what you want. If you type \wrappic{flower.jpg}{this is a rose!} no scaling is applied.
In general, using scale= is discouraged, as it depends on the size of the picture and you'd need to adjust it manually. I'd propose something different:
\newcommand{\wrappicauto}[3][\dimexpr\textwidth-1em\relax]{%
\par\noindent\mbox{%
\begin{minipage}{0.3\textwidth}
\includegraphics[width=#1]{#2}
\end{minipage}%
\begin{minipage}{0.7\textwidth}
#3
\end{minipage}}
\par}
so that
\wrappicauto{flower.jpg}{this is a rose!}
will scale automatically the picture to occupy 3/10 of the text width minus a small separation space.
If you need a different width, then you can say
\wrappicauto[3cm]{flower.jpg}{this is a rose!}