Regarding the simple substitutions section just to prove your point about not going overkill i benchmarked the two ways you mentioned (tr and s) as well as just uc with this code

#!/usr/local/bin/perl -w
use strict;
use Benchmark;
my $count =500000;
## Method number one
sub One {
   my $data = 'for bar baz';
   $data = uc $data;

}

## Method number two
sub Two {
   my $data = 'for bar baz';
   $data =~ tr/a-z/A-Z/;
}
## Method number Three
sub Three {
   my $data = 'for bar baz';
   $data =~ s/([A-Za-z]+)/uc($1)/ge;
}
## We'll test each one, with simple labels
timethese (
  $count,
  {'Method One UC' => '&One',
   'Method Two TR' => '&Two',
   'Method Three s'=> '&Three'
   }
);

exit;
[download]

And got these results:

Benchmark: timing 500000 iterations of Method One UC, Method Three s, 
+Method Two TR...
Method One UC:  1 wallclock secs ( 1.42 usr +  0.00 sys =  1.42 CPU) @
+ 352112.68/s (n=500000)
Method Three s: 16 wallclock secs (17.03 usr +  0.00 sys = 17.03 CPU) 
+@ 29359.95/s (n=500000)
Method Two TR:  1 wallclock secs ( 2.04 usr +  0.00 sys =  2.04 CPU) @
+ 245098.04/s (n=500000)
[download]

I know this is not new information but i figured i'd post here to highlight what you are saying.
PS -- The bechmark method stolen from Benchmarking your code

UPDATE: Xxaxx pointed out to me in This Node That I am not making a fair comparision above. The eval of uc($1) in the s/// regex was eating up a lot of the cycles. The gap is smaller than 17:1 shown above...
For a fairer test I compared a single char substituion with tr/// and s///

 my $data = 'for-bar-baz';
   $data =~ s/-/_/g;
   print $data;
 my $data = 'for-bar-baz';
 $data =~tr/-/_/;
 print $data;
[download]

Using the benchmarking above I got hese results:

Benchmark: timing 500000 iterations of Method One TR, Method Two s...
Method One TR:  2 wallclock secs ( 1.87 usr +  0.00 sys =  1.87 CPU) @
+ 267379.68/s (n=500000)
Method Two s:  5 wallclock secs ( 4.84 usr +  0.00 sys =  4.84 CPU) @ 
+103305.79/s (n=500000)
[download]

Still there is an advantage to tr/// over s/// which can be more noticable depending on your data.

Update 2: petral asked me question in the CB about the way i call uc in method one made me realize that it wont actually do anything because I don't assign the return value back to the var. I updated the code to do that.