Base Stock Speakers

[OldGuy]

I'm not much of an audiophile and actually the sound from the stock system in my 370Z base sounds adequate, though not remarkable, to me. The local stereo shop guy says that for under $100 plus cost of installation, two new Kicker speakers in the front would be a great improvement for a modest amount of money. If, it's true as he says, that the factory speakers are very low grade and speaker upgrade is the way to get the biggest sound improvement for the least amount of money, maybe I should do it. Does this sound right or should I just figure he's trying to make a quick buck and leave well enough alone? Also, he says new speaker grilles will be installed. Does all this create or increase the potential for a rattle or two? Could I get an opinion from someone who has done this or knows more than I do about audio (which would be just about anyone!). Thanks in advance.