Turns out, atea does all I need and integrates nicely into the OSX UI with an icon in the menu bar. It does:

  - project-based task management
  - proiority ordering of tasks
  - Dropbox-based syncing of one or more task files
  - time tracking
  - comparison of real times to estimates

So, in the end, maybe it is actually the perfect solution, and it is free, too.