A technique I often use for this sort of problem is to have the regex work its way over the problematic section one character at a time and use look around assertions to handle the quoting. Consider:

use warnings;
use strict;

my $line = qq{Test #1 'Show me Waynes world','Jennys Basketball shoes'
+\n};
print "< $line";
$line =~ s/(['"]).+?(['"])/$1SSS$2/g;
print "> $line";

$line = qq{Test #2 'Show me Wayne\\'s world','Jenny\\'s Basketball sho
+es'\n};
print "< $line";
$line =~ s/(['"]) (?: (?! (?<!\\)\1 ) .)+ \1/$1SSS$1/gx;
print "> $line";
[download]

Prints:

< Test #1 'Show me Waynes world','Jennys Basketball shoes'
> Test #1 'SSS','SSS'
< Test #2 'Show me Wayne\'s world','Jenny\'s Basketball shoes'
> Test #2 'SSS','SSS'
[download]

Note that I removed to redundant sprintfs, showed before and after versions of the test strings, and fixed the quote issue in the second test string.