I’m really enjoying the math nodes, and I would like to use them for vectors/rotators as well, but it is cumbersome to have to break a vector just to insert it into a math expression node.

Is it possible to specify the input of a math node to be a vector/rotator?

Select the node, then look at the ‘Inputs’ section on the Details panel on the left. You can change the pin types using the dropdown menus. You can see an example in the screenshot I posted.