It is worth buying if you want it. Try to catch it on 50% or the really rare 75% sale for the best value.
It adds a bit of content that breathes a little life into your games with storms and other items to ruin your and your enemy's days.
Something that will make it worth 100% worth it is if you use the Online features of Sins,
They have it setup so that the host shares his DLC with all player joined, an especially fantastic feature and I'm glad Stardock included this! Same applies to Forbidden worlds.
I would have troubles recommending this at full price but, in reality it adds some basic functionality that can move a locked up game. Useful for singleplayer especially.
7/10 a Useful DLC that breathes more life into your solar system but may not be worth it at full price.