Thanks for the suggestions! That "doit" looks like it's simple enough for my fairly pedestrian needs. I wonder if my aversion to Make is that I don't spend enough time thinking/making Makefiles, but having something a little friendlier and simpler -- at the cost of ubiquity/portability -- might be the kind of training wheels I need.

Edit: FWIW, I posted doit to r/python and someone suggestion Snakemake, which also looks excellent and well-maintained: http://snakemake.readthedocs.io/en/stable/