I use FXP 319 and the picture quality is the best.in daylight is not better than old 4.1.2 (.36 if i recall well),but in low light is way better.The photo just has more detail in it,not too much noise,faster capture.
The time also removed that UV protector or whatever it was from my camera lens and I didn't noticed any difference.For photos aganist the sun just use HDR and you're good to go!
For now,I don't think they worked a lot on camera,but from what I've read FXP 324 should be a big release and I hope they'll fix everything about camera.
Also,there are some rumors about jellybean 4.3,so maybe Sony will provide us after all the best camera performance...or it will be a big disappointment as all the updates release by now.
All the best !