I have an old HP8714B 3GHz VNA. It's only a T/R VNA but I've developed a method to get good 2 port s parameter data from it. However, this involves mucho swapping of connections and use of attenuators for the S21 and S12 measurements.
I get the raw vector data via GPIB and then gradually build up a 2 port s parameter file for S11, S21, S12, S22. I've also created my own user cal files for it to enhance the accuracy when taking 2 port data.
It takes a few minutes to do it all.
It has the biggest/nicest smith chart display of any VNA I've used but I do want to upgrade it to something like a 6GHz 8753ES. I will miss the nice display of the 8714B when I upgrade and I've been using it for so many years (at work and now here at home) that I've grown quite attached to it
I have also recently bought an old HP8405A vector voltmeter and I sometimes also use a simple 2 channel scope and a sense resistor or a coupler to make vector measurements with a scope.
I'm playing around with negative impedances at the moment eg negative capacitor and negative resistor circuits and the HP8405A VVM is an ideal tool for this