I would say that it would be most helpful for you to get out into the field and start applying those ABAP and WebDynpro skills you've aquired. It took me two solid years of doing ABAP development to really understand all of the concepts that I use on a day-to-day basis. I'm six months into doing WebDynpro and it's definitely going to take me another six before I have a solid understanding.
I took Workflow training a couple years ago and at the time I understood everything, down to the advanced development and administration concepts. It was all very interesting, but because I haven't used it in the years since, I would hesitate to say that I now have even a basic understanding (the kind you get from the first chapter of a book on Workflow).
Long story short: If you have to take some training, Workflow is good. But it would be much better for you to get years of experience using ABAP and WebDynpro first.