Paradox's DLC have been more akin to "mini-expansions" with some cosmetics on the side (unit packs, music packs, etc...). I've generally ignored the latter, which I don't care about in any game. I don't mind the model so much here as it keeps the game fresh for quite a long time, but Paradox do have a knack of messing with things that are perfectly fine to the point where your game is often ruined if you take the patches and don't take the DLC. EU4 for example I thought had a sweet spot just after Art of War came out, with El Dorado not doing much and Cossacks really messing with the game.
Still, after finally seeing some gameplay for Stellaris, I'm definetly excited.