I always gave those stat boosters to Sora, especially those that boost attack and defence. Selfish, I know, but I don't think giving them to Donald or Goofy would make any difference. Because of their AI, they would still be knocked out not even ten seconds into a boss battle.
You'll get the option to synthesise more of those items, though, if you really want to. Just make sure that you do so when you've listed every single synthable item, because I remember somebody here being unable to unlock further synthesis items because he used up too many Mythrils before Mythril itself became available for synthesis...