Well, I finally found Camera Zoom FX for my Eris and have been comparing against the FXCamera app. For taking quick processed photos, I'm not as impressed as I thought I'd be. It appears to still downsample the image when you use any kind of effect, so that isn't an advantage over the small images that FXCamera produces.
It looks like Camera Zoom FX might be better for taking normal photos than the built-in app, not sure. But the most useful effect I would usually use is called 'Toy Camera' in FXCamera. This makes it look like an old toy or lomo camera, and is kind of nice for otherwise boring shots. I haven't found a way to really duplicate this effect in Camera Zoom FX. It has a cross-process effect, but it makes the shots way too blue overall. And I can't see a way to apply a vignette at the same time. So I'll usually prefer FXCamera for 'effected' shots.
However, I've briefly played with an app called PicSay. It looks REALLY nice and powerful for adding effects after the shot. May use the built-in app or Camera Zoom FX in normal mode, then use PicSay to do effects.