While I have not yet changed the dash speakers, my opinion would be that they are probably going to be the easiest. To access them, if I remember correctly, you'll only need a torx tip screwdriver. The center panel closest to the windshield just slides forward, which reveals the torx screws of the side dash panels. Simple.
Yeah, changing out the rears won't do much unless you add an amp to give them a bit more power. The stock Monsoon system is very front biased, and it sounds like you already figured that out.
