Anything that you can't farm for energy is pretty much guaranteed to be worth the cost in shipments.
Of the things you can farm for energy, more often than not, it is actually cheaper to buy them out of shipments than to buy the energy.
Purple gear has a drop rate of 1/3. At 10 energy a battle that's 30 energy a fragment. That's 4 fragments per energy refresh. 5 refreshes for a 20 piece purple piece. 50+50+100+100+200= 500 crystals to farm a 20 piece purple piece that you can get from shipments for 300 crystals. You can say: "but wait I get 375 energy a day so I don't need to buy 3 of those refreshes" Fair enough, the FIRST piece of 20 piece purple gear each day is worth farming with energy. Once you get your two 50 crystal energy refreshes though, it is actually cheaper to farm gear from shipments than to spend energy.
For a 50 piece that is 13 energy refreshes. If you got them all for 100 crystals each that would be 1300 crystals, but you can't get them that cheap unless you spread it out over several days. Fusion furnace actually needs closer to 100 pieces. 1400 crystals is a VERY good deal for it.