They make a biiiiiiiiig difference.
Changed mine recently, couldn't believe how shoddy the standard ones are.
Fiddly to get old ones out as they are held by two screws but windscreen is right in the way, obviously put in before the screen at the factory! Also a tight fit to get new ones in as they are deeper than the standard ones.
I got some pioneer ones off ebay for about £20, 100W.
Also replaced the door pocket speakers with some uprated 130W pioneers (originals had stopped working!) and the rear 6x4 speakers (either side of the parcel shelf) with some infinity's.
Sound quality's 10x better now!