While my personal preference is for sentence case, I do have one minor positive point for title case I’d like to raise.
For UIs that use words very sparingly, such as in its buttons and dialogs, title case makes more sense. I find that writing in title case helps keep my copy relatively consistent and uniform, as it immediately looks odd when I try to use too many words.
I do stray towards over-verbosity at times, and sentence case can be quite indulging…
Anyway, great write-up, so thanks for sharing!