I've had old cars with the same problem, and the difference when you swap out the speakers is pretty noticeable. It's not just that it gets louder, you actually recover frequencies that the stock system just doesn't reproduce. On the Aveo you especially notice it in the bass and voice clarity if you listen to podcasts or audiobooks.
Now, the key is not to buy just any cheap kit from the mall. Those generic kits usually come with mediocre components and the installation is a headache if you don't know how to solder or don't have the tools. If you're gonna do it, look for brands that at least have decent reviews (Alpine, Kenwood, Pioneer), even if they're pricier. Also think about whether it's worth dropping cash on a 2009 Aveo or if you'd rather just live with the crappy sound until you get a different car.
My recommendation: if you actually listen to music in your car, go for it. If it's just background radio while you're driving, it probably isn't worth it. And if you do decide to do it, have someone who knows what they're doing do it; a bad installation can mess up your electrical system.