I almost NEVER set up my tarp. I almost ALWAYS sleep out under the stars. I do most of my camping in the rockies, and the evenings are cold enough that bugs are not an issue.
I camped a fair amount this summer, and NEVER ONCES set up the tarp. I simply ALWAYS slept outside (I had good luck with clear weather)
NOT setting up a shelter on a clear night means I save time, and see the stars.
I NEVER need to change at night - so it's easy getting in bed, and the same in the morning. I can get up and there is almost nothing to pack. I have ALL my clothes on, so I simply start hiking. I stop when I get warm and eat breakfast and brew up coffee.
I do NOT cary extra clothes to sleep at night. the clothes I have on are synthetic or wool (quick to dry) my body oils are all next to my skin (under multiple layers of clothes) so nothing to make a bag "oily".
Also - the *extra* clothes that some carry should be (more correctly ) called pajamas.
I do use a bivy sack. It weighs under 6 oz, and I use it with a quilt (19 oz) so my bivy / quilt combo weighs 3 oz LESS than your 28 oz sleeping bag.
If I had a 20 degree sleeping bag and a SpinTwin tarp, I feel that a bivy sack is not needed, the tarp is big enough to protect a down bag from the rain.
But, with a tiny quilt, a UL bivy is really nice. (I love my bivy-sack too)
I have (very rarely) used a mosquito head-net to sleep. I wear my baseball style hat, put the head-net on, wear ALL my clothes (3 layers of hoods!) and the bugs are never an issue.