Most rule changes are in the hope of speeding up the game. This rule of saying the score out loud & precise I go along with but not "I believe" etc. This is totally unnecessary. If the opp. disagrees with the score get them to put their hands up to stop the serve & then discuss the problem

Please don't do this. I believe this is overkill and unnecessary.

This is really an interesting proposal. There are always things that go wrong with serve-calling.
1. Opponents can't hear (often because the server doesn't call it loud enough). So you have cases of the reciever not being ready and caught off guard.
2. The "quick-serve," the server serves at the split second after the third number is called. Legal? Yes. But if the score is called wrong, bad things sometimes happen. (remember, not all players are famiiar with the rules, and then arguments ensue).

So, there could be a case made for a change here. Not quite sure I agree with asking the reciever a question, but I always teach my players to:
1. Call the score loud enough so your opponents can hear. If you are unable to, have your partner call the score.
2. Wait a second or two after calling the score to give your opponent time to argue.

Could be some merit here!

Although it is important for players to call the score loudly enough for opponents to hear, this is an unnecessary change. Just as in officiated play, if a player is having difficulty hearing the score call they should ask their opponents to adjust either the volume or how they call the score (e.g. using hand signals rather than just verbal signals).