Dev,
There are a couple of directions you can go - you can work on building new 'skills' (or enhancing existing skills) like the ones listed as Competencies in the BABOK, or you could work on learning new tools and techniques (such as UML, BPMN, diagram types, etc.).
The BABOK is a good place to start for either skills/competencies or for techniques that are most directly related to typical BA roles. If you're more interested in going outside the BOK (forgive the pun, I couldn't resist) then I can suggest a few complementary areas to consider. Since you mentioned that you are responsible for developing wireframes, you could build expertise in usability and user experience best practices. There is growing demand for these skills. Data modeling can also be a useful skill for BA's (goes way beyond the brief coverage in BABOK). You could also explore some of the modeling techniques that are becoming popular such as decision modeling (several good articles on Modern Analyst). Faciliation, conflict management, and negotiation also come in very handy. Building knowledge of testing practices and techniques is also helpful - even if you're not responsible for testing, you'll write better requirements when you understand what's involved in testing the functionality that gets built from them.
You mentioned UML - this is a standard notation language / technique that is usually adopted as a project or organization standard. It extends beyond requirements artifacts (such as activity diagrams and use cases) into the more 'technical' ones such as data models and software components. So you could certainly learn about UML, but you might not have much chance to practice it if it's not a standard for projects in your company.
My suggestion is look for skills or tools that best match your personal strengths and interests. You'll get the most benefit if you build to your strengths, and you'll have more fun that way too.
Sandy