The last upgrades aren't necessary. Just max them out to master level.. You'll run into countless high level locked containers and storage rooms locked by high level terminals with for the most part sweet loot... I can't stress this enough

But none are plot ending, presumably.

You miss out on loot, but you can still progress the quest...

Didn't find them that necessary. Not that many to be troublesome, especially with my Brotherhood Power Armor + Gatling Laser already

Maybe if they contained a suit of T-51 or Gatling Laser with Science 4 upgrades