I am actually replaying PoR and RD for both the story and to do it on a harder difficulty. For all my playthroughs of those two I never payed attention to story or side conversations. Now I am playing on the hardest difficulty and listening to every info, support, character vs character conversation, etc. Yea, it takes longer but I enjoy the immersion.
To answer whether or not it has replay value, well, kinda. Yea, if you don't know the story much then listening to the conversations can really fill you in on what was happening and why you are in certain places and fighting certain enemies. I wouldn't replay it just for the story, but paying attention to it for the first time, it is really interesting to me.