They make a difference, but compared to the other stock sound systems we have in our other basic cars ('94 Toyota Camry LE, '13 Honda Accord LX, '08 Hyundai Elantra GLS), they still don't even come close.
I'm especially surprised by our '94 Camry's audio system at how decent it is (had it since new since 1994) compared to these Kicker Upgrades, which are a a few points better in my opinion.
We also have a '97 Toyota Corolla DX, the bass blew, but I would say these Kicker Upgrade have around the same quality of sound as the Corolla's before they blew.
I was thinking about adding in the Alpine Power Pack amp system to boost the power a bit, but overall, I just got used to the Kicker's after a while so for me it's not worth putting into it more.
If they do come out with a new STI without the EJ257 motor anymore, and hopefully an FA motor of some sort, I'll just trade this in and go for that with the Harmon Kardon