"very few of us appreciate all the productive uses of all of Perl's features, especially outside the problem domains in which we are comfortable."

The fact is that nobody will really wonder into every corner of Perl, or any other language. For languages like Perl, Java or Ruby, which tend to have specific modules to cover lots of specific function areas, you never have the need to cover all of them, although you might occassionally open up couple of modules to see how other people do things.

Not only those specific modules, even with the basic functionalities, there is never a need to use all of them. Not only that you don't need them, you actually should intentionally avoid some of them. Almost all languages, more or less, have some functionalities that do more harm than good. It is more important to learn best practices and stick to them, than to utilize the full language.

"What do other people do to hone their Perl skills"

Lots of practice with the best practice in your mind.