Ralph Lorenz at the Johns Hopkins University Applied Physics Lab is a planetary scientist with a keen sense of wit. He's written a story for Space Review on the joys of reviewing the 28 Discovery mission proposals submitted to NASA. Its worth a read both for the insights into the effort required to develop these proposals as well as the writing style.
Lorenz has a long list of solid contributions to mission design and planetary science. He's also taken the lead on some fun investigations such as the dynamics of Frisbees and why rocks seem to move on their own across the Death Valley.
As for the size of Discovery mission proposals, one proposal's principal investigator has shared with me a section of his team's proposal. From the table of contents, the body of the proposal is 120 pages with another 285+ pages of appendices. I am in awe of the effort the planetary community has put into producing 28 of these proposals. That's an investment of what is likely a few tens of millions of dollars between them for a competition that will have a single winner.
Lorenz also brings up a problem that the number of proposals produce. So many scientists and engineers are directly involved with or are otherwise associated someone on a proposal team that it likely is hard to find a large pool of qualified reviewers. I talked with a lead on a proposal from a few years back. He told me that the comments received on his proposal suggested the reviewers weren't experts in the area of study proposed. All the leading figures in the field were on his proposal team and therefore couldn't be reviewers.