Cisco,
Most of BAs would pay to do the work that you do: Working with business stakeholders and gathering requirements. Now the old DFDs are a good medium to work with in particular with Business Stakeholders because they understand them intuitively.
Use Cases are disjointed, they tend to only show behaviours that are governed by the business requirements. And a swag of Use Cases are difficult to understand on there own, they need some kind of workflow that tie them together.
For workflow, you can either use UML Activity or BPMN diagrams. Both are rich definitions of how to define process and its prudent to reduce the features used when dealing with Business Stakeholders.
You are one of the few BAs that actually create ERDs and an accompanying data dictionary. You should be commended! I trust these ERDs are at the logical level.
How do you up-skill depend very much on where you want to be. Now DFDs and structured analysis are no longer in vogue; they don’t teach it at most universities and people frown at you when you mention it. But don’t be deterred.
May I suggest that you download a few tools and have a play; it beats having to read books. Start with what you know, so download http://www.casecomplete.com/Features.aspx. This allows you to learn extra value add things like traceability and creating User Acceptance Test plans. A really good BA should be able to test what he or she has specified.
For BPMN diagramming, download http://www.Bizagi.com tools and the Definition from OMG. Download their free process diagrams at http://www.bizagi.com/index.php?option=com_content&view=article&id=171&Itemid=186 and have a play. Convert some of your existing swim lanes activity diagrams to BPMN.
Move onto http://www.sparxsystems.com.au/ and download 30-day free enterprise architect. Not a shabby tool indeed. Its allows you to do all the above plus ERDs and LINK them together. There are probably other tools that can do similar things, but I have used most of these tools (except casecomplete).
Now if you really want to, you could go and buy some UML, BPMN and ERD Books
Have a good Weekend. Our weekend is especially long (Friday till next Tuesday- inclusive)
Warm regards,
K