blockdiag doesn't do clipart, but it does many different shapes, colors, etc. including rounded corners if you want them.
It's not the right tool for every job, but it does a lot more than you seem to think it does.
and it scales very well. I was able to throw a network structure with 135 networks, 600 devices, and around 3K interfaces at it and it was able to create a diagram from it with the nwdiag tool