I would suggest that proposals offer useful hints and links to information and concepts, but I would recommend against spelling the proposals out in significant detail. The reason for this is that sometimes students will do an excellent job of either regurgitating or paraphrasing a proposal. It then becomes more difficult to figure out if the student really knows what they are doing (or not).
If the written proposals offer a direction and some stepping points (only), then the students have a chance to "fill in the blanks" and it becomes much easier to identify these "better" students. Just my opinion. H