I've got to correct my previous post.
Apparently, either I misread or Cryptic changed it, though my money is in my misreading.
I was sure that the offers in the doff window were one for 100 additional space for doffs, and the second for 25 additional mission doff slots, that is, increasing your simultaneous running doff missions from 20 to 45.
As it is not so, and you are limited to 20 missions, adding 100 additional officers, even 25, serves no purpose. Right now, one of my toons has enough doff mission packs to fill 50 personnel slots and like 8-10 missions that reward 2-3 new officers, but if I want to keep increasing the "recruitment" cxp bar, I need to keep doing missions and getting more officers, which I don't have any place to put them.
But 100 officers is enough for those 20 mission slots. As long as there is no way to run more missions simultaneously, adding doff crew slots is mostly pointless.
By the way, the change with the latest patch that allows to see your chained missions progress is nice.