In terms of actually hiking, I'd always consider a thin down jacket as being a mid-layer - put a hardshell on top to keep it dry and provide some protection from rucksack straps. It's also more versatile in that you can opt to wear it or not, depending on temperature or level of exercise during the day, and packs down small when not in use.
By and large, though, I wouldn't wear down for actually walking in - to my mind fleece or some other more robust mid-layer/outer is better for that, tougher and much more tolerant of moisture from inside or out. And down can be too hot - even walking in -15 degrees in the Alps, thermal base layers, a couple of fleece mid layers and a waterproof shell have been plenty warm enough.
Off the hill, my favourite cool weather jacket for dry conditions is a Uniqlo ULD jacket - small, packable, breathable, not too warm going from outside to indoors, and about £50.