I do that too. Since my Pearl has an ungodly amount of pokemon stored, I'm not transferring the pokemon and restarting that file. In addition, I still have event pokemon to pick up, such as Deoxys and Dragonite, which I'm not going to any time soon. Therefore, Platinum will also be my restart game.I won't stop playing my diamond version. Every generation I get at least one game to restart over and over and one game I keep and try to complete everything in. Platinum will be my restart game and Diamond I'll continue to try to do everything in.