As for other ways to make questions writing easy, here are a few:
* Enable to copy answer trees - one branch to the same tree, or an whole tree to another answer. It turn out most of my time is spent on writing and debugging similar trees again and again, making sure I did not forget to fill in the marks correctly and so forth.
* Enable to copy test - this way we will be able to write the test in terms of variables defined in the question, and thus will be able to copy test for similar questions.
* Create an answer test that enables to rank a numerical answer based on the numerical precision (such as, you get 50% of the points if your answer matches the right one to one order of magnitude less then the desired precision, and 25% to two orders of magnitude) - will reduce answer test tree size.
*Enable mark to depend on the value of a certain variable, in the answer test.
* Enable copying a question also from the quiz page (rather then the question page) - I don't know if this will be a stack feature or a moodle feature.