Welcome to the dorky world of JRB quilts!
I have been using the Sierra Sniveler for 1-2 years now and more recently took it with me on the JMT in August.
I have not gotten rid of my mid-layer insulation, Montbell Thermawarp Jacket, simple because there can be rare occasions where I find that I will want a jacket to hike in if it is fairly cold....shoulder seasons.
Plus, I often find that to keep the chill off my shoulders while sleeping under the quilt, I will wear my Thermawrap.
I think that you could selectively decide to leave your insulation layer at home, depending on the weather conditions you expect to encounter, like in summer time.
I error on the side of safety and I am a cold sleeper, so I take my jacket with me all of the time.
That said, it is great to be able to wear the quilt in the morning while having breakfast to stay toasty warm.
Looks dorky as hell and sitting down while wearing the quilt can be a problem with the edges of it spilling out everywhere.
Hope this helps.