[Giller]

Good door speakers will add a lot of sound to the cabin - definitely worth the upgrade. They will help with those lows.

But yeah, while in there, might want to consider just doing the whole thing and adding some rear speakers. They too make a huge difference and since you are running cable all around anyways. And I found it a fairly simple DIY if you have the parcel shelf back there. Just need a few 3.5 speakers.

You can also go crazy and add a powered subwoofer. Kenwood makes one small enough that sits nicely underneath the passenger seat that delivers an okay sound. Definitely helps with the lows.