To an extent that is true but some are built well with a good class D amp. Also, our cars are tiny inside so it won't take much to fill the space with bass. I've been down the road of big 12" enclosures and 1,000+ watts and I'm kinda over it - and with two kids in college, so is my wallet!
This past xmas I got a gift certificate which i used for a set of
Hertz DSK 170 63/4" for the front doors. NOT AT ALL what i would recommend for bass as they are purpose built mids but my plan is to eventually fill in the bottom end with the powered 8". I'm going for fidelity on a budget.
And OP, don't forget a quality sound processor to flatten the wacky EQ curve from the OEM setup. I've got my eye on the
JL Audio FiX™ 82. I looked at the
FIX 86 for the front/rear fading but it's outta my budget. But if you're going with separate amps for front/rear/sub then it's highly recommended.