That would be more like: „Doceniamy twoją odpowiedź”/„Doceniamy waszą odpowiedź” – not exactly the same thing.
Just checking and likely a silly question, is waszą in accusative or instrumental here? I'd have to assume accusative but "za" sometimes takes instrumental. If instrumental, I'd expect to see "odpowiedzią"
"za" takes Instrumental when it's "behind" something.
"za" takes Accusative when it denotes movement (I am going behind the house = I am on my way to end up behind the house), and when it means "for" (paying for something, thanking for something, etc.) Maybe something else that doesn't come to my mind now. Anyway, this is Accusative here.
I guess it's because "thanks" is informal. It's often translated as "dzięki", the word you can use talking with friends and not in formal situation.