Shavuos- Holiday of Introspection

Shavuos, like the other Jewish Holidays, goes by a number of different names. One of those is עצרת, Atzeres, a name which it shares with the Eight Day of Sukkos which is commonly referred to as Shemini Atzeres. Other than a name the two holidays also share another unique feature. They are the only holidays on the Jewish Calendar that have no mitzvos which we are commanded to do on those days (other than special karbanos mussaf brought in the Bais HaMikdosh. We are referring here to mitzvos incumbent upon the masses.) Is there any connection between the shared name and lack of mitzvos to perform on these days?
I would suggest that each of these holidays comes after 51 days of spiritual effort. Beginning with Rosh Chodesh Elul we focus our energy on Teshuva, reparing our relationship with God. This takes us right into Rosh Hashana and Yom Kippur which are replete with mitzvos followed by a week and a half of building a Sukkah, acquiring a lulav and esrog  and then dwelling in the Sukkuah. As that holiday season comes to an end the Torah wanted to ensure that we didn't get so caught up in the doing of the mitzvos that we never spent the time thinking about them and integrating them within ourselves. Therefore there is one day that is עצור ממלאכה, on which we have no specific tasks to perform. We can spend that day contemplating our experience over the past 7 weeks and making sure we walk away with something meaningful that will last.
The same is true of Shavuos. Ever since Erev Pesach we have been busy with mitzvos. We have prepared for Pesach. We have experienced Pesach  and then entered into the time of Sefiras Ha'Omer. There is room in this entire process for much growth, but, again, we can get so lost in the details of the actions that we neglect to make sure that we take something home with us. Hashem has given us Shavuos for that purpose, to stop, contemplate and integrate so that all of our actions and efforts in each holiday season remains with us for the remainder of the year.