What you describe is a CSV (character separated value) file and there are a plethora of modules available to handle that format for you. A good starting point is Text::CSV. Using such a module your problem turns into:

use strict;
use warnings;
use Text::CSV;

my $dataStr = <<DATA;
1/1/1923\tFirst entry\t-23.45
2/2/1924\t"Second entry with a long multi-line description.
This is parsed fine using Text::CSV, but I bet your regex chokes."\t23
+.23
DATA

my $csv = Text::CSV->new({sep_char => "\t", binary => 1});

open my $dataIn, '<', \$dataStr;
while (my $row = $csv->getline($dataIn)) {
    my ($date, $description, $value) = @$row;
    
    print "Value is $value\n";
}

close $dataIn;
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Prints:

Value is -23.45
Value is 23.23
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As an aside the regex magic you want is the ? modifier:

use strict;
use warnings;
use Text::CSV;

my $dataStr = <<DATA;
1/1/1923\tFirst entry\t-23.45
2/2/1924\t"Second entry with a long multi-line description.
This is parsed fine using Text::CSV, but I bet your regex chokes."\t23
+.23
DATA

open my $dataIn, '<', \$dataStr;
while (my $line = <$dataIn>) {
    next if $line !~ /(-?\d*\.\d*)/;
    
    print "Value is $1\n";
}

close $dataIn;
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Prints:

Value is -23.45
Value is .
Value is .
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which you will note still fails in nasty ways because the regex isn't near sufficient to extract the data you want. However, there are a huge number of errors in the regex you show so you absolutely must go read some of the regex documentation: perlretut, perlre and perlreref for a start.