Having removed all mine the sound is the same, with or without the covers, as for the thermal insulation, the sides and front panels are just plastic and would have little or no thermal quality, the centre piece would maybe have a small amount.
As for the covers in general, I think that all major motor manufacturers now use these covers and my opinion is that it's done to make under the bonnet seem mystical in some way,, you lift the bonnet and see all these covers and think to yourself,,I'd better take this back to the dealer to sort out.
And I reiterate my original point, if the covers are removed you have a chance of spotting something amiss with the car.
you pay your money and you take your choice.