How to improve student seminar presentations and seminar papers
This sounds exactly like the situation we are experiencing at our university as well. We have improved the situation by forcing the students to write papers and similar texts every semester (starting from semester 1), in different settings, and we're giving detailed feedback afterwards. In our first and second semesters we are using this setting for one course:


Students can select one topic and prepare it in a group of three (the idea is to mix people so they can give feedback within their group). We emphasize that everyone will receive a grade based on personal efforts and success, and there is no group bonus / malus. 
They will present the topic in a group of three (20 min presentation + 10 min discussion) 
We are giving a 3h presentation on scientific writing.
They have to give their paper outline to their supervisor after about 3 weeks. The quality of feedback depends on the effort put into the structure. If they hand in "Introduction, Main Section, Conclusion", they will receive a "correct, but good luck" ;-). 
They shall hand in a first version after about 50% of the course. This version will be discussed in a personal feedback session of one hour by a scientific journalist
At ~3/4, they have to submit their "pre-final" version to a conference management system. 
Everyone is now switching roles and becomes a reviewer. Every reviewer has to review two papers. The quality of reviews is part of the final grade.
After the reviews. the groups have one more week to finish the final paper submission.


As said, we are following this highly intensive approach in semesters 1 &amp; 2. In the subsequent semesters, we are having other settings, but we force them to write every semester. It seems to bear some fruits since the quality improves over time, but it's clear that we can't fully repair what went wrong during school...