Welcome to the forums, and to the game
I'll leave the question of whether it's worth it to the players, but just to make sure you know what you're getting for your $5 (4.50 or so on steam right now, I think, during the first week) :
* Champions.
* 2 new map types. Clusters is my favorite now.
* 2 new AI types. They're very hard, though, so if you're just getting into the game it may be a while before you want to try them.
* 9 new bonus ship types. With the alien bundle you don't really
need more bonus ship variety, but there are some really fun ones in here like the Tackle Drone Launcher (my new favorite) and the modular "bonus starship" Spire Corvette.
* Modular Fortresses.
* New Dark Spire minor faction. Again, very challenging, you would want to learn the game without it on at least for now. But major chaotic fun potential.
* 3 new AI Core Guard Posts; you won't see these til the AI homeworlds, though, and it might be a while before you see those.
* A whole bunch of new music from Pablo Vega, and the general consensus I'm hearing around here is that it's his best AIW work yet.
Anyway, my suggestion would be to download the expansion and play a trial game on a clusters map with Tackle Drone Launchers as your starting bonus ship, and a champion. If that doesn't catch your interest, probably just wait to get it later, but I think you'll like it