After "run-in" time, no. The only time an amp can truly sound different between the first time it is powered up and subsequent times is if it breaks.
"Break-in" of electronics is a myth...the equipment works the same. We're the ones who "break in"...it's all in our heads (and it's a great way to get people to keep equipment, especially overpriced snake-oil cables, past the return window.)
As for the sound of the amp itself, the only way to truly ascertain if an amplifier has a different sound is in a level-matched double-blind test...that gets the human perceptual biases out of the way. That said, if your old amplifier was an old unit with aging caps and deteriorating performance a new amplifier would definitely be an improvement. But so would a rebuild of the old one to bring it back into spec. But bringing home a new component is always fun, and there's no reason to deprive oneself of such pleasure.
Cambridge does make a solid little integrated, there's nothing at all wrong with them, and they drive difficult loads fairly easily due to their stout power supplies. 600-series B&W's should be fairly easy loads though...
Regardless, you have a good little amplifier that should last a long time. Enjoy the music!
