Totally agree Pete, VNAV is not really the mode to be concerned with when you are being vectored, particularly from a base leg vector.
Sometimes relying a little too much on the boxes to give you situational awareness can lead you up the garden path..so to speak.
Far better IMHO, is to have some basic DME info available..and a basic understanding of the geometry of the current heading vs distance to the centreline....which will also give you a better situational picture..plus has the added bonus of developing a feel for estimated track miles.
Failing that..a quick peek on the EHSI in map mode should give you a good idea as well!...then there is is the banana bar for the cda etc etc
Ahh how I miss my Boeing banana bar...
