Ive noticed that many character concept designs use a splochy water droplet texture effect for the backgrounds (Looks almost like airbrush sputter) ... I cant seem to figure out the right brush/texture settings to get this effect. Can anyone help?
I'm not entirely sure what you're asking for in your description, but this was achieved with photographic brushes, i.e. someone actually sputtering ink and scanning it. I don't know where these brushes are from - I believe I picked them up from a compilation on HOON's Mess Studios but he doesn't say where he got them from - just a lot of surfing. He lists a 19 mb collection of random brushes on Mess here.
You could always make your own by taking a stiff bristled brush and some ink or tints and sputtering away, or I'm sure you could find a whole heap of similar brush packs.
Like I said, custom brushes very likely at use there. Gradient or blurry painted background, splatter brushes at medium opacity overlaid (normal, multiply, colour or linear burn) a few times (turn on angle jitter). The artist may or may not have run a pass of gaussian blur on top of the pic, depending on the crispness of the original brushes.