When I was purposefully going for rank I only did as much as required to unlock the ships. Rank grinding back then took much longer than it does now, so I had no desire to prolong it.
However, in the years since then I've wound up both Admiral and King just from doing whatever took my fancy at the time.
On one of my alts recently I did some Empire rank work, because I wanted a Clipper. I was amazed at how quickly it went. Times have improved muchly in that regard.
I don't know - I remember yonks ago ranking up real quick at Tun's Wart just donating credits - left a bad taste though but I suppose these days courier-hopping in the boondocks is just as soul-destroying.