You wanna know the other awesome thing about Sins of a Solar Empire: Rebellion? The mod community is pretty awesome. Some I'd suggest checking out...
A spiritual continuation of the Armada series. You can play as the Federation, Klingons, Romulans, Borg or Dominion (which includes the Cardassians and Breen). They have release 1.0 out, it's pretty damn stable AND very nice to look at. The animations are pretty top notch, and the play is nice and fun. The Borg are a tad overpowered, but they're working on balancing that better. Suffice it to say if you let the Borg get going they become very challenging to stop. It was PC Gamers Mod of the Week a couple weeks back (March 15th, 2014).
Another example of a Star Trek modification. I personally prefer Armada III but this is well done also. They're both very similar but have slightly different play feel to them. Personally SoA feels more like building a fleet (ala SINS) and the above mentioned Armada III plays better with smaller fleets, more like you'd expect Trek. It's kinda hard to explain.
If the Star Trek flair isn't your cup of Earl Grey, Hot, then might I suggest a Star Wars flavour to your Sins? SoaGE is a very decent Star Wars total conversion. You've got six factions to play as, they're the major sides in each of the Galactic Civil War (Episode IV, V & VI so the Galactic Empire and Rebellion), the Clone Wars (Episode I, II, III and the TV Clone Wars Series, so the Confederation and Old Republic) as well as the Yuuzhan Vong War (that's from a book series, you are either the intergalactic invading Yuuzhan Vong or the New Republic). I enjoy it quite a bit, and the Star Wars universe lends itself particularly well to Sins.
Another Star Wars Mod for Sins. Just like the two Star Trek ones I shared this is also in the same flavour as the above mentioned Star Wars mod. Just some minor play differences and different factions / ships. I do prefer this one to Sins of a Galactic Empire, but to each their own! Both are extremely well done.
Lets break out of the SW / ST theme for a moment and touch on a different Star, Star Gate! This mod has been in the top 100 mods for all games as voted on ModDB.com for 2010, 2011 & 2012. It missed out on 2013 because the Mods had taken some time off and just recently updated it to be compatible with Rebellion. It allows you to play as the Tauri (Humans), Jaffa, Asgard, Wraith or Asuran (no, not the guys from GW2). It's also pretty slick and a lot of fun.
Well those are the mods for SoaSE: Rebellion I've found that were actually worth playing. There are some other ones up on ModDB.com. You can brows all the Sins mods right here if you're looking for something else.