By learning the classics, especially those that are radically different from what you already know, you expand your mind and your sense of what is possible. It helps you get a different perspective on any given problem you may run in to, having seen radically different approaches to similar problems in the past. It puts another tool in your toolset and lets you select the best tool for the job.

Not that the above is not possible to get with exposure to hot new technologies, but whatever's hot in the market tends to be much more of a monoculture and popular due to being not too different from what most developers already know (Clojure and Scala being perfect examples).