I'm nearing the end of Borderlands 2, and there are some side quests ranked trivial that I would rather not bother with. I have some of the SDUs from the black market, but not all of them.
I'm not concerned with missing out on some level 20-25 unique blue or purple stuff; I am concerned about starting a second playthrough and being cut off from some SDUs or otherwise unattainable upgrades, permanently. Can this happen? Are there any permanent upgrades that occur once per playthrough and are not available from the black market?