I completed the Pokedex in Platinum and I have so much good stuff on that 300 hour save. I really wanted to play through it again, but there's no way I'd want to erase that save, so I bought a new one.
I did the exact same thing. Platinum was such a good game that I felt I had to.
I also have two copies of SoulSilver, but one is Japanese and the other is English, so I don't know if that really counts. And then I had two copies of Crystal for some reason, but lost one of the copies at some point. --- STOP CALLING ME HOME ROWED i don't even gaf anymore