I bought a base G35 thinking the stock system would be adequate, but apparently I was wrong. How can I get better sound out of the stock system? I don't want to get crazy with an amp and subwoofer. Would swapping out the speakers yield a noticeable improvement in sound quality?

 

Worth a shot. You'll probably get the biggest difference from a sub though.

 

Most aftermarket speakers are made to produce highs and mids, if you only switch out your interior speakers you will loose what bass you do have now.

 

given that the g has tweeters in it you would likely need new crossovers to ensure you have a nice low, mid and high range sound but in short, yes, you will see vast improvements if you buy some decent speakers and have the right crossovers.

i just installed a 10 inch sub i had from my last car in my g35 (it's been sitting waiting in my basement over a year!) and personally i think it made a big difference. in reality installing a sub is way less work than installing new speakers all around.