Flats, but with good soft soles (I ride 5.10 Free Riders) with pinned pedals. I still ride SPDs with my road bike, but have switched to flats with my others.

Emergency acceleration? Pulling up on the pedals? Haven't really felt the need for either while touring, but do the former quite regularly with my flats in other riding situations. Do the latter very rarely, and then only when sprinting or really straining up a serious grade. Can't remember ever needing to sprint all out while touring, and the lower gearing with my touring bike us what handles the grades.

If you like SPDs then no need not to go with them, but they're not necessary for touring.