I keep my games. It would have to be really horrible or defective for me to return it. This generation is the first one for me to ever return a game because it was bad though. I know I'll eventually want to play each game again in the future (I still regret selling my Gamecube), so I pretty much have to keep them.
No, I don't have them all hooked up at the same time but I wouldn't retire them just because they aren't plugged in. I still have my original Xbox plugged in and my Genesis is sitting in a drawer only because I don't have he cable that plugs into the TV anymore. I would have a SNES, PS1 and N64 if they didn't break from family use many years ago.
I sold my Gamecube and games and sincerely regret it now so I don't think I could completely retire a console, plus, I plan on buying a lot of the older consoles soon.
I got the same ending when I first played the game. If I remember correctly, it doesn't really change at all if you go for another ending. Depending on which ending you are going for, the only thing that will really change is the dialogue between you and the final boss and the identity of it. It's still the same boss fight Also, on your second playthrough there are some extra items that you can get, special weapons depending on your rank of the last playthrough, secret items to get another ending and extra options but that's about it.