"I am always curious about which rituals people would keep for their own reasons. Would you be willing to share any other mitzvot or traditions that you would still follow, without anyone telling you to but because they are meaningful to you?"
My big ones are kashrut, Shabbos, and a host of traditional holiday stuff.
Kashrut, even if Mis-nagid says it is a social control, which it may be, is still a big aspect of our Jewish heritage and does have positive effects (as well as acknowledged negative ones) like a stronger Jewish community.
Shabbos is tradition to the core and I also really like the idea of a day without worries. People don't realize how nice a thing it is to not have to worry about making sure you have all sorts of "important" stuff in your pockets before you leave the house. It's a small example, but that I don't need to take my keys and wallet and cell phone with me where ever I go Shabbos afternoon is incredibly liberating.
Besides, I also think a family meal or two each week is important for obvious reasons and the entire air of an official day of rest takes the cake. I get all my best reading done on Shabbos.
Holidays are important as far as culture is concerned and most holidays would not feel "real" to me if they didn't come along withdoing traditional events. I _like_ building my succah. And I like the seder. I even appreciate the concept of fasting on days of real pain for our people and gives the day a sense of importance and our connection to history. (It's sad that most fast days are taken up with stupid discussions about "Are you still fasting?" and "I fast easiest when..." and all the crap about the actual stupid fact off asting and never about why we fast. People don't get it.) I can't imagine not fasting on Tisha B'Av.
Holidays are important.