3 April Updates show as Important on 1 PC and Optional on another

I checked this one only, Event 55 when you copy an encrypted folder to EFS shared folder in Windows so if one is using EFS and the other not, it could be optional on the one that does not use EFS.

Nothing is wrong with either one, it depends on the software you have and how it's used that makes the updates Optional, Important or Critical.

It may be due to the different security and Office 2013 you have. I have no concrete answer. I have 3 w7 Ultimate machines and each one is offered different updates.

Critical updates are generally only severe Security ones, or fixes for major problems causing BSOD's
The variation in optional/important could be due to a number of factors - among them
1) installed software
2) attached hardware - printers, external drives, etc
3) machine history - MS appear to be using some event log history to manage updates, which may cause an update to either suddenly appear, or to be upgraded from Optional to either Recommended or Important.

It may be worth looking to see if there are any USB-related errors in the event logs with the machine showing the updates as Important, as the first in your list is related to problems with USB devices, and the second could also be related. (Both iSCSI and Smartcard devices often hang off an internal USB port in the machine)