How is this question of mine "too broad? Is the importance of planetary science for Earth science so enormous that it can't even be explained? Then please just answer so, don't shut it down. How am I supposed to rephrase the question?
Part of the issue is you are asking many questions. From your post I see:
Has planetary science contributed in any substantial way to Earth science?
Is it expected to do so as planetary exploration develops in the next few decades?
Do climate scientists know about the atmospheres of Mars and Venus and Titan and the gas giants?
Are they interested in following such discoveries?
Do seismologist use data from the seismic experiments on the Moon during the Apollo program?
Do they look forward to the NASA Insight lander on Mars next year, or is it considered irrelevant?
Does an orbiting and landing mission to a comet teach us anything about Earth science?
What kind of interplanetary mission would be the favourite for Earth scientists?
Some of these questions are related, but together they are very diverse. In particular, questions (1) and (8) are broad, some can be argued to be opinion based and some are fine questions on their own.
The Q&A model SE is based upon uses posts asking a single, focused question that has an answer. Asking multiple questions that aren't narrowly related makes the question too broad. Asking open ended questions that you could write wikipedia articles about are too broad.
You have a wide variety of questions. My advice is to break down your post into multiple focused questions. Take out the ones that solicit opinion or are too broad on their own and ask the rest each in their own questions.
It is too broad because it would take an entire book to answer the question, because the importance of planetary science for Earth Science can be addressed from many different perspectives. There could be easily over 100 different answers to that question. On Stack Exchange, we want questions that can be answered in a considerable shorter space.
You can phrase the question differently to be much more specific. For example, you could ask specific questions on climate models for Mars. Or specific questions on how spectroscopic measurements of the atmosphere of Titan affect spectroscopic measurements on Earth. Or maybe on how observational techniques developed for astronomy and space science are used in Earth observation (sub-millimetre comes to mind). But in each case, please be specific.