they are pretty weird to write. i would be serious but it doesn't necessarily have to be your manifesto of life.

I have had to write plenty of covering letters for job interviews. For the actual writing I tend to first bullet point what I want to say in each paragraph and under each one list the points I want to get across. It's essential that each point is as direct and brief as possible. Once I'm happy I will go through writing out the points as full sentences and paragraphs. For me this splits 'what I'm trying to say' and 'how do I phrase this' out into seperate tasks; making it easier.

where is the line between talking like a lazy politician and saying what you want to say?

Be direct, but not cocky or arrogant. Padding out sections makes them dull, boring and implies that your statement is just quantity rather then quality. Avoid this at all costs.

I would also aim to answer: Why that university?, why that course? what makes you a good candidate for that course? why re-join university? what has changed (i.e. why will you not drop out this time)?

Answering all of them should be enough to fill a whole page. Finally I highly advise doing as much research as you can about the uni and the course, drawing on this throughout your answers in order to relate your skills/experiences/interests to the university and the course (i.e. that your made for this course).