The short answer is "yes."My last car, an `06 Ford Freestyle LTD had WAY better audio reproduction than my CT does. Not that my CT audio isn't good... I still think it's better than most.
With that said - I once heard that speakers are 80% of the stereo... and Good quality speakers will sound 20% better.
Now my question is this... with car audio starting to be so high in quality... Can just simply chainging the speakers (direct swap) improve the audio w/o adding amps, crossovers, or disabling ANC?
However, it can start to get more complicated especially when systems (such as our CTs) have active noise reduction systems, etc.
(at least this is my understanding)