The 'minimum of 1 damage' isn't really for ship combat (as noted it's in a different section). The problem is that 'ground' combat is at a range where you can realistically aim for a given 'bit' of a person or vehiclel there's always a chance of striking a track/lens, or joint, with a sufficiently good shot. Space combat is speed-of-light slow and ultimately comes down to plastering the mathematically predictable possible location of the enemy ship with sufficient random fire; aiming for a given point is more or less impossible.
High Guard is intended as the sourcebook for capital ships, and big, high-tech naval combat.
If you intend to have major ship battles in your campaign (i.e. more than a couple of traders pot-shotting away with lasers) it's something to get hold of as a priority.
It is, however, part of the System Reference Document - i.e. the bit freely available for third party reference, so the key bits of rules changes (if not the careers, artwork, ships, etc) are easy enough to find.
The main extra bits are:
Armour limited to TL.
Options for 'Primitive and Advanced Spacecraft' where Hull and Structure vary with TL for the same size.
Options for high TL drives, weapons, etc, which either take up less space or perform better (but cost more!).
A metric shed-load of new options, from emergency back-up power plants to external docking clamps, and more new weapons than you can shake a sandcaster at, up to and including the 14,000 dTon, spontaneous-existance-failure inducing, Spinal-Mount Meson/D cannon.
The 'barrage combat rules', for resolving entire wings of light fighters or broadsides of several dozen turret mounts, which aren't as bad as a lot of people think (once you get your head around what they're trying to say).