My main account had a glitch where I didn't get Dooku from the DS starter pack (since resolved), but while I was waiting for that to work out I started a second account where the Dooku purchase worked. In 3 weeks of farming shards I have gone 0/6 many of the days, while the best I have ever gotten is 2/6. I am at 23/30 for getting him to 4* - and like I said, that's after 3 weeks.
Regardless which "Hard" mission I try to farm 1/3 is a good day for me. Over half of the days I go 0/3. Cantina seems to be more reliable for me where I almost always get 1/3 on average for the day.
That's based on 2 accounts - $5 spent total in each of them, for what it's worth.
