As far as my group is concerned, they are all not worth buying.
No harm in letting the Sardakk player buy all three should they wish is what we decided.
Exotrireme would like a word with you...in regards to Muat War Suns, Nekro Alastor or Sol/Nalu Carriers...
while "situational" it's actually a pretty nice deal. One damaged dreadnaught flat-out DESTROYS 2 enemy ships you chose. While i have no serious love for the Norr, i like having that option around...in offense and defense-the first time you blow up an invading carrier and ask WHICH ground forces/MU's he wanted to take that planet with, you'll never forget.