Answer to Question 1
Additional schooling makes sense, if the expected marginal benefit is at least as large as the user cost. If I am close to graduation, and diploma capital contributes much to my expected income and/or valued competencies, the additional investment may be warranted. Even if graduation is a distant (or irrelevant) goal, the human capital I've acquired this semester might enhance the expected benefit of further schooling. I know the explicit and implicit costs of an additional semester, but will the knowledge I might acquire increase in value over time, or depreciate?
Answer to Question 2
A