Kant would agree, and went further, saying that people should always tell the truth, "even if it meant saving a friend's life from a murderer" and that it was an unconditional moral duty https://en.wikipedia.org/wiki/On_a_Supposed_Right_to_Tell_Li...

Contemporarily we have methods like radical honesty - another moral absolutist take that also asserts a primacy of truth, that as long as you tell the truth, you can do no wrong

For a lie always harms another; if not some human being, then it nevertheless does harm to humanity in general, inasmuch as it vitiates the very source of right... All practical principles of right must contain rigorous truth... Kant

So, that's the moral side of things. Whether or not you believe in truth as a moral compass (or even a component of it or some moral rubrik), I'll leave up to you! What you said:

> But if I am not really grateful, then my words haven't conveyed information about an actual experience

...gets more at the utility of honesty, as a conveyer of experience. While I might argue you still have conveyed an experience (just not one you had), because the references and end experience still happened in the mind of the receiver, the end (target) experience was had.

The invention of lying is largely due to it working just as well (or better than) the truth in the first place. Maybe the first lie was an accident, and evolution took over where only the best liars passed on their ideas.

So that you could even have an experience rich enough to contemplate!