I lean toward lightening my pack without sacrificing warmth, since I tend to sleep cold. I have never liked synthetic sleeping bags, jackets or vests. I prefer down. I have a Marmot Helium sleeping bag, rated to 15 degrees, which means I'm usually cold if it gets down to 30.
But it's a very nice bag, and I tend, at my age, to avoid camping in weather colder than about 40 degrees at night. I didn't used to avoid this, however. Anyway, this bag weighs 2 pounds and packs to the size of a small watermelon. I got it on sale (you will cringe when you see the regular price). I use a down vest, but am thinking about buying an SUL (superultralight) down jacket as well. I want one of the kind that packs up really small. I always use a stocking cap.
Down is a lot lighter than synthetic.
I haven't done much lately to lighten my pack since I have been doing more kayak camping this past year, instead of backpacking. But if you buy something heavy you will replace it later. So you may as well buy something light and good now. Check out ultralight websites. REI is not very good at this yet. Gossamer Gear, Six Moon Designs, ULA, Mountain Hardware, etc. etc.