My aveo audio upgrade

At the beginning of the year I put in my aveo TS-M800PRO speakers with silk dome tweeters along with one shallow mount pioneer ts-swx3002. all the seats, panels and carpet were removed to install dyno mat everywhere. the build was a success but lately the panels them selves have a couple loose things i want dealt with. The audio shop suggested i replace the panels with fiberglass instead, and install one more set of the pioneer 8 mid woofers in either doors. My question is what are the benefits of adding a second set of those 8's to my doors. would the difference be super noticable, or subtle? will i get more bass or vocals? if anyone has upgraded something like this any info would help. thanks!