Responding to positive grant reviews?

If there's no criticism to rebut, then waive the right to rebut.

If you've already received top marks with no criticisms, then you can only spoil things by saying something at this stage.

Just shut up. And enjoy the moment.

While it sounds that there would be no need to rebut against anything (I suggest to read the reports very carefully once again - some criticism can be hidden and is sometimes difficult to spot between positive comments) there may be another reason to formulate a response. It may well be that the reports contain valuable suggestions or remarks on specific points of your proposal. You can take the opportunity to pick up these suggestions and present new views or deeper explanations. However, I think that this really only makes sense if you have something new to say in view of the comments of the reviewer. I would suggest to not repeat what is already written in the proposal…