1) The fact that Rashi does not comment on the repetition of all the details of the mishkan that we find in Vayakhel/Pekudei seems like a glaring omission. The case of the dog that didn't bark, as Sherlock Holmes might say. Rashi comments on the repetition of the story of Eliezer's encounter with Rivka (Braishis 24:42), so why is the repetition here any less bothersome, any less deserving of explanation?
(The L. Rebbe speaks about this question.)
2) וַיֵּ֥צְא֛וּ כׇּל־עֲדַ֥ת בְּנֵֽי־יִשְׂרָאֵ֖ל מִלִּפְנֵ֥י מֹשֶֽׁה׃ (35:20)
The Torah ordinarily does not mention that class was dismissed, so to speak, and the people went home when Moshe was done speaking. It goes without saying, or should go without saying. So why is it mentioned here? See Netziv.
My son on his blog writes:
Rav Elya Lopian says that you could tell on the faces of Bnei Yisroel that they just left Moshe. Being in the presence of a Moshe Rabbenu changes a person and that change must be present in the viewer's life. He says this a mussar for the end of the zman. Those entering bein hazmanim must carry with them the appearance of those that just came out of yeshiva.
(See there for an amazing pshat on parshas Shmos based on the same idea.)
Fair point, but why does the Torah single out this instance to bring it up? The same point could be made any time Moshe spoke to the people.
Also, compare with "Vayeitzei Yaakov mi'Beer Sheva..." There Rashi comments that the departure of the tzadik left an impact on the place he departed from. Here, the idea is the opposite -- Moshe left an imprint on the people with their departure from him.
R' Eliezer Sorotzkin (quoted by his son here) also addresses this question and suggests that the yetzi'a here is not just a "davar shlili," which would not be worth mentioning, but the yetzi'a is significant because it is to do a dvar mitzvah, to collect for and start building the mishkan. The Torah is telling is that Bnei Yisrael took heed of Moshe's words and carried out his instructions.
Still a bit difficult because it was not leaving Moshe's presence which was the mitzvah, but rather the positive act of engaging in making the mishkan. So why not emphasize the positive and tell us something like "Va'yasu Bnei Yisrael..." or "Vayeilchu Bnei Yisrael...?"
There is a comment from another Sorotzin -- R' Zalman Sorotzkin, in Oznayim laTorah -- that sheds more light on things. The Oznayim laTorah raises another interesting question: The parsha opens by telling us that Moshe gathered all of Klal Yisrael to speak to them, וַיַּקְהֵ֣ל מֹשֶׁ֗ה אֶֽת־כׇּל־עֲדַ֛ת בְּנֵ֥י יִשְׂרָאֵ֖ל וַיֹּ֣אמֶר אֲלֵהֶ֑ם. He then speaks about Shabbos, and then 4 pesukim later we again have וַיֹּ֣אמֶר מֹשֶׁ֔ה אֶל־כׇּל־עֲדַ֥ת בְּנֵֽי־יִשְׂרָאֵ֖ל לֵאמֹ֑ר, and Moshe starts to speak about the mishkan. Why do we need this second וַיֹּ֣אמֶר ? The whole point of gathering all the people (see Rashbam, Ramban), as mentioned in that first pasuk, was to speak about the mishkan. Pasuk 4 is not a new idea, but is a continuation?
He suggests as follows: when it comes time to give a fundraising speech, no Rabbi calls together his congregation telling them that's the topic. Who would show up knowing that's the agenda? What the Rabbi does is give a nice derasha on some other topic, and then once he has the audience hooked, he sneaks in the appeal.
וַיַּקְהֵ֣ל מֹשֶׁ֗ה אֶֽת־כׇּל־עֲדַ֛ת בְּנֵ֥י יִשְׂרָאֵ֖ל וַיֹּ֣אמֶר אֲלֵהֶ֑ם to give a nice shiur in hilchos shabbos. Now that Moshe had his audience captive, וַיֹּ֣אמֶר מֹשֶׁ֔ה אֶל־כׇּל־עֲדַ֥ת בְּנֵֽי־יִשְׂרָאֵ֖ל לֵאמֹ֑ר he switched topics and hit them in the pocketbook to appeal for funds for the mishkan.
The thing is, as clever as the Rabbi is, the audience knows this trick as well, and so what happens is that as the Rabbi meanders through his opening topic, the crowd will begin to dwindle. This guy has an important phone call to take, the next guy davka then has to rush home to help watch
TV his kids, another guy suddenly remembers he set up a seder with some chavrusa that he hasn't met in a year, but no time like the present, etc. By the time the Rabbi gets to the appeal, he is talking to the few stragglers who probably are not the people who can write the big checks.
יֵּ֥צְא֛וּ כׇּל־עֲדַ֥ת בְּנֵֽי־יִשְׂרָאֵ֖ל מִלִּפְנֵ֥י מֹשֶֽׁה׃ -- here, EVERYBODY got up to leave at the same time, at the end of the speech. No one snuck off in the middle, before the appeal started or was over. Klal Yisrael was willing to listen to Moshe hitting them up for money, and they proved more than willing to give.