I've always seen and used "That's a great question!" and similar vacuous phrases when speaking as a polite way to buy some time while formulating an actual response to the questioner.
That's a good question... => I didn't think about this, I don't know the answer yet.
That's a great question! => I can tell you understood what I explained and used that understanding to reach the next step of reasoning just like I did.
That's a great question! => I can tell you understood what I explained and used that understanding to reach the next step of reasoning just like I did.