It definitely adds weight. I did my entire 4runner...ripped out the seats, carpet, headliner, all panels, etc. Rig got a helluva lot quieter. I'm sure over time that my door hinges would weaken.
This time around I'm just gonna do the two front doors where I will have speakers. I'm using MB Quart QSD 6.5 drivers. They will be playing down to 80hz. If I don't use this stuff the door will rattle to pieces. Not to mention the doors will eat up any sound quality that the speakers put out.