I'm a huge fan of ember tetras. Not sure about the soft water comment. My water sits at 7.4ph and 4dkh and my embers school tightly and display a brilliant red with the females being very very deep red. I had 6 embers and 5 panda cories in a 10g and they were fine for a year or so, now it's 16 embers and 5 pandas in a 40B same water parameters.
I don't know if I would call a scarlet badis a "centerpiece" fish... I find that they like sheltered areas in my tank, so I'm always having to look around for them, whereas my CPDs are always out and about. I love the color and activity of the CPDs, even if they don't school very well.