Well, I think you need at least a basic knowledge about those two. DataAssist have some great tools which simplify a lot of tasks. In my opinion, DW should have provided some of these. Because if you look at it, since Dreamweaver MX there has not been a lot of innovation on the php/mysql server model. I don't know this for asp or others, though.
And this is where DA and other tools come in. They fill the gap and although rather costly, they abbreviate the construction process. So, in my opinion its worth.
Sometimes they have annoying bugs which are not always easy to find. But as far as I am concerned, Ray and his team are really doing a great support job here.