In the FLEX API, there is something called a composite symbol. This let me layer two different lines or point symbols, which acted as one. I used this extensively as a way to highlight a feature the user had selected, because I could take the existing symbol, but add a yellow highlight by adding a symbol larger than the current symbol.
I don't see that anything at all like this is available in the Javascript API. Am I missing this, or is this something that could possibly be added in the future?