I think your body's appearance is partly controlled by your emotional state. I feel and look a lot sexier after a shower or exercise or something that makes me happy. Perhaps being happy, stress-free etc. increases circulation throughout the body via endorphin release and in turn the body's more "toned and awake"?
Yes. Some nights when I shower my penis looks big and strong while some nights it looks smaller. Maybe it does actually change sizes from night-to-night or maybe it's just my imagination. But sure there are days/nights when I look better than others. I think everyone has those days.