Ok, this may be a worn topic by now but here is my opinion. Tony is a collector. He is collecting the suits cause he is proud of being Iron Man. It puts him in the spot light. He collects cars and motorcycles too, all in his garage. He could display a hologram of the cars he likes but he is filthy rich so why not go buy the cars he likes... same with the suit. I think Nick Fury even says something about his OCD personality. So do you think he would have all but one or two suits? Nope, he rebuilt it to have/own/collect it.
Now I have to agree on the Mk III. It shouldn't have the damaged chest plate... they should all be in pristine shape. This seems to be out of character for him. However, maybe he left the chest plate damaged for an unrevealed personal reason. Maybe he left it like that on purpose to remind him that he is not invincible or maybe to remind him that Obediah betrayed him and he needs to be more careful about letting something like that happen again. That is the closest he has come to dieing in the films.
Also, I am not sure where I saw this... it could have been in the movie, perhaps some behind the scenes footage, or maybe just a BTS photo but I do remember seeing the crushed helmet at the feet of the Mk III which was on display in his Hall of Armor.