Are military buildings worthless? And more.

Hyperion military buildings can be very OP. Read this!

As to the Defensive military buildings, they are so so. You can make you planets immune to invasions with the right combinations though.

By using the right adjacency bonuses using Elerium shield, anti-matter reactor, pragmatic building and a military resource as well as a couple precursor military improvements, a surrounded Hyperion Shrinker will give you up to 40% mass on all your ships. I would say that is useful.

To reinforce Horemvore's statement, if you surround an Elerium shield with a planetary defence and the pragmatic building that gives extra resistance combined with the right defence tech you make your planet invulnerable to invasion, particularly useful in a game with tech trading turned off since your opponents cannot trade for the other invasion techs. On your valuable planets such as the precursor or paradise ones it is pretty much required, the AI keeps trying to invade and keeps failing, useful to draw down a particularly strong opponent

Although your original ships get percentage bonuses from some sensor specializations, to get really noticeable sensor range, build new boats with the newer sensors and better base sensor values.  Then the percentage bonuses will have something to work with.  It takes both factors to really get anywhere.  The mechanics involved are meant to make sensor range a challenge, but it is worth the effort. Gotta see 'em to shoot 'em!

As others have indicated, they can be either crap or broken OP. A single defensive building is worthless, but 2-3 of them with stacking level bonuses can make a planet virtually immune to invasions. If the AI doesn't have biological warfare, they basically cannot take your planets.

Sensor Range is no longer a flat linear number, like Speed is.  This is because the AREA a sensor sweeps out is just as important as the linear range. Sticking with a linear range meant that every increase in Sensor Range brought a increasing amount of area with it, which is seriously OP. For example, a +10% bonus to Range actually increases the total area seen by 20% (1.10^2)

Rather, the new concept of "SensorPower" was introduced, which attempts to take into account this problem. In order to have a Range of X, the arithmetic sum of X in SensorPower is required. The math is such:

SensorPower required = (Range)*(Range +1)/2

All bonuses are now to Sensor Power. So, a +10% bonus to SensorPower is much less likely to increase Range. In particular, small bonuses are unlikely to change Range except at the very low end (when you have NO sensors) or when you're near a boundary (i.e. when the SensorPower you have installed isn't quite enough to make the cuttoff for the next Range).

In short, Sensor Bonuses in percentage will generally only provide a +1 Range for those ships with no sensors (even for very large bonuses). For those ships with moderate Sensor Range (ie. 4-7 or so), these will be the ones which you see the biggest benefit from, with large SensorPower % bonuses translating into 2-4 extra Range.  Once you get about about 10 "native" Range, you are really going to need about +25% or so to see a +1 Range bonus.

Sensor bonuses make the most impact for ships with 2-3 sensors on them. Below that, you'll either see +1 or none, no matter how much additional bonus you research. Above that, you'll occasionally see a +1 range, but it won't happen with every additional Sensor bonus.

It's all about the math. 

I dont know why they dont have long range sensors.... they detect moving ships at a great distance, it tells you nothing other than ship size - any ships not moving they do not detect. So you wont know which race or how powerful it is etc etc.

It may even be a way to make it harder for the player to sneak around the AI, since the AI could be programmed to try and investigate all approaching ships. they certainly spam enough junk to do that job!

I'm a more peaceful player who rarely goes to war. I use military buildings only for two reasons

1. to buff the hyperion shrinker and other such special buildings, like the Arcean Navigation-Buildings etc.

2. to increase a planets resistance to culture flipping if I buy, colonize or inherite a planet within another influence zone. However that is only temporary, I destroy them as soon as the danger of culture flipping is gone.