People hate on this DLC too much. It's added in a lot of features, moddable features at that, that add a lot of depth to the game, in particular to base Sins.
The fact that there are four new planet groups allows for a wealth of planet mods to make plenty of planet groupings rather than having to rely on the few that are currently ingame, which is something that has adversely hit mods in the past, such as the famous Sins Plus.
The specialization system allows modders to make planet features, such as a bonus to ship construction time, a part of a planet's entity itself, rather than coding it as a passive ability, which will result in RAM savings.
Plus there have been new options added to planet bonuses, such as an increase, or decrease, in the number of star bases and mines that can be built, and in the maximum allegiance a planet can have.
Heck, I don't even plan to use the DLC in my own modding, but it's pretty damn clear that this DLC adds a wealth of possibilities for modders to use and exploit.