So you're wondering what hot young thing you want to get to know this summer? Is she going to be JSON, MongoDB, WebGL, or maybe Node.js? The reality is The Business doesn't care. The Business only cares about one thing and one thing only: that you're driving value-add moving forward. Getting to know Clojure is only so much developer indulgence; The Business doesn't care, and they only see that it will make you more valuable to some other employer instead of them. You are better served learning all the intricacies of the ancient information system that's mission critical. Learn all the contradictory layers and business rules that have accumulated over the years. Learn what keeps it happy. You should be a SME, a go-to guy The Business can call on when it has questions. Then learn about Gantt charts and a bit of project management. The all-coveted tower of Lead is found on a path through these. You will code less and sit in meetings and on bridges more. You may even add a process of your own to the bureaucratic machine.
Look to your elders. How did they become Leads and architects? It wasn't by learning new technologies, APIs, and languages; it was by understanding The Business, respecting the chain of command, following process, and paying their dues. Just play your role as a well-greased cog in the corporate machine and grind on and on.