You’ll note that I considered the inflated ship as an interesting alternative idea that should definitely be experimented on. That said,
It is not the game that is asking you to be efficient, it’s the players (and designers) that are asking the UI to be efficient. A good measure of efficiency of the UI is how much you think about it, for example, the less the better.
This is why FPS HUDs look more like Half Life’s than Doom’s, for example.
Icons (when done right) are good at giving the important information fast without obstructing the view. Look at a fighter’s HUD: while primitive by game design standard (many are at least 20 years old, and militaries tend to be conservative on top of that), they don’t obstruct view that much or look that cluttered.
With modern game design and aesthetic experience, you could get a pretty transparent UI (as in, you don’t think about it) that shouldn’t hide the game proper (and its great looks) much.
Now, let’s come back to this inflated ship idea. In essence, they pretty much are evolved icons. Instead of drawing an abstract or stylized shape representing the ship, you draw the ship itself.
What information does it bring?
Like icons, it tells you there is something there, and where it is (I’m assuming both are done in a way that shows the order of distance).
Like icons, it tells you what it is - for icons by identifying the shape and remembering what it is associated with, for ships by direct identification. Note that identifying a ship can be harder than identifying the simple shape of an icon, because a ship is a more complex object that require more effort to analyse. This is why I recommended drawing its silhouette and/or simplified wireframe on it as well - the simpler shapes would give a fast identification, while the ship itself would still be visible.
Unlike icons, it shows its orientation in 3D, simply by looking at where it is pointing.
Unlike icons, if there is visible damage or visible activity, you can identify it. So you know if it is fleeing you at full-speed, or if one of its engine has been blown.
As a disadvantage, though, it may make harder to see what’s happening with several close targets, as overlap would be worse. When you see a bit of a triangle, you know it’s a triangle. When you see a bit of a ship, it can be harder to guess what ship it is.
Another disadvantage is that you cannot rely on icon shape to identify friend and foe - and colour may or may not be relied upon, as it must be playable by colour-blind people.