What tips out there with Perl do veterans have to try to understand how such large plates of spaghetti function? I have leaned heavily on the caller function and Data::Dumper. What are the suggested power tools?

I find Devel::Cover a great exploratory tool for unknown code. Write some tests that exercise the functionality you're interested in. Look at the coverage output to see what code was touched.

Anything to help generate any sort of UML type pictures?

For the automatic UML rendering try UML::Sequence and UML::Class::Simple.