I believe that because your mind is more awake when coming out of a vivid or lucid dream, it carries over so that your mind is ready for the day and already active. Also I think that it lets you observe the process of waking up better so that you are more in tune with what is actually happening. Things such as an increase in heart rate, the changing of your brainwaves, your organs starting to function more readily. Thus giving you a feeling of euphoria you wouldn’t normally get if your mind wasn’t conscious enough to observe it. But thats just my scoop of the poop.
Also, when I do have a lucid dreams it definitely makes me feel more accomplished, and that gets me thinking about it all day.