Don't know why a single statement is preferable, but this may do the trick:

>perl -wMstrict -le
"my $s = q{' * + [] {} '};
 print qq{[[$s]]};
 ;;
 $s =~ s{ (?: \A ['\"])? (.*?) (?: [\"'] \z)? }{\Q$1}xmsg;
 print qq{[[$s]]};
"
[[' * + [] {} ']]
[[\ \*\ \+\ \[\]\ \{\}\ ]]
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Update: Got rid of /e regex modifier and  quotemeta call, used \Q string modifier instead; removed some runaway backslashes.

Update:  s{ \A ['"]? (.*?) ["']? \z }{\Q$1}xms is simpler, makes use of /g modifier unnecessary (after jwkrahn).