I've become a great fan of Devel::StealthDebug (except the name).

use Devel::StealthDebug;
...
#!dump( $var, \@foo, \%bas )!
...
#!watch( $volatile )! ## Only traced when it changes.
...
----outputs----
$ $var = 7;
$\@foo = [
  123,
  456,
];
$\%bas = {
  'a' => 1,
  'b' => 2,
};
 in Test::new at Test.pm line 31
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Comment out the use line and all the tracing disappears. It can also be enabled/disabled by use line parameter, environment variable or presence/absence of a filename.

No run-time intrusions at all when disabled, but easily re-enabled. Watches are especially useful for cutting down the volumes of trace, though can be a little temperamental. That's only scratched the surface of it's capabilities; it also has #!assert( condition ), #!when( varname, op, value )! and #!emit("sometext")! pragmas.

It's dump() format is preferrable to most of the dumpers-that-wannabe-serializers I've tried, and it doesn't exact the huge memory overhead that serialisers require for circular reference detection when dumping complex structures.

It's also filter-based, but like you, I don't have a problem with that for debugging purposes.