Could you use threading to speed up bulk processing of documents?
Can you use some new package or gem to improve your day to day development flow? (for example, i just found a rails gem that helps speed up start up time for rails tasks, totally using that at work)
How about your Version control, are you using the latest techniques or type of software?
What about learning more about dev ops, how to manage the server and do little things here and there without bothering the server guy?
What about search, are you writing contorted sql queries to hit the databases for your search, or are you using elasticsearch, solr, sphinx or lucene which are better suited for those things?
Is your logging app writing to file logs, or (worse your RDBMS database) or could you use mongodb to speed that up?
Are you analyzing data you collect in an insightful way or is it time to read up on some analytics tutorials, to come up with smarter ways to inspect your data?
how fast is your software? Could it be faster? How can you make it faster?
etc etc etc
In the end it comes down to your curiosity to learn and try new things. That will help you keep abreast of new ideas and help you spot opportunities to apply them sensibly. It should get you from where you are until the point where you feel that opportunities like these are exhausted, at which point, its time to move on.
Never let yourself stop growing as a developer.