Congratulation on being an expert. No, seriously...
I've been doing drupal for almost 10 years on and off every year, but
I feel I don't even come close to some of the people with the vast
amounts of knowledge here.
No one does something for 10 years without gaining some expert, or near expert, level proficiency in something. Obviously, that statement depends on the body of knowledge in question, but to put that in perspective, Drupal will be 15 years old next year; you've been working with it for 2/3 of its entire lifetime.
In fact, that statement has a nice meta-statement to it; you realize the extent of your knowledge and take for it granted; you know what you know and that there's always more to learn, especially when it comes to Drupal. If that doesn't show some command of expertise I don't know what does.
The prosaic truth is this; in a complex open-source system no one person can know everything. The expertise comes in mitigating this problem. This is where I think more soft skill come into play. For example:
- Knowing where to find canonical sources of knowledge.
- Having a network of people to touch when you need to utilize skill X
- Understanding the quirks of a project's community
- ...and list goes on with other nice skills to have in the discipline of software development/engineering.
As for places to go, you probably know all the active places where experts are at: d.o. forums, issue queues, DrupalCon (as well as other OS cons), g.d.o (if you're local community is big enough to support it), IRC chats, and of course, Drupal Answers (if there are any other cabals of Uber elite Drupallers please let me know otherwise :).
The only other piece of advice I can think of is this; once you've hit the boundaries of knowledge (or at least you feel that you have) start forging your own path of new knowledge; join a project that really interests you or create your own. If for nothing else, you will gain some new knowledge & experience in interacting with others.