I think you may be onto something. Especially as someone coming from a Christian background, the word gratitude is deeply intertwined with the concept of Divine Grace. It's also connected to 'giving thanks' , but thanks to whom? Appreciation on the contrary, doesn't imply you appreciate to someone, but rather, at something. And that thing you are appreciating is the feeling. Your insight instantly and intuitively seemed very helpful to me, I will certaintly use it in my daily pratice.