I also prefer a down bag. The one I use for bike touring is a North Face Blue Kazoo that I bought in 1976 and have used on multiple times each year since then. Yes, it must be kept dry, but that has yet to be a problem. And I consider it more of an issue for winter backpacking trips where lack of a usable bag could easily be life threatening. When bike touring there are usually options available if the worst happens and the bag gets soaked. Mine is rated to 20 degrees and I've used it with reasonable comfort down to 0 degrees with a VBL. On warm nights I just leave the zippers open and only partly get into the bag - or not at all if it's really hot.

In comparison to synthetics, I find that down still allows for a more compact bag when in its stuff sack, a wider comfortable temperature range, and better durability when properly washed and maintained.