I'm a total Valencia fanboy/apologist/whatever but this rings true for any footballer. In my opinion there is just no excuse for being one footed. Especially if you're a professional training every day, hitting the gym, honing your skills as a full time job.
I was completely one footed when I played football as a kid. Completely hopeless with my left. Just couldn't use it, but all it took was practice. I became determined to strengthen it when I was 13. I remember hearing an interview with Chris Waddle which really resonated with me. He started out as being completely 1 footed, but he worked on his weak foot, strengthened it, practiced everyday, just kicking a football against a wall constantly. That's pretty much all I did. I don't play at a high level obviously, but I feel as confident in my left as I do my right foot. I play a fair bit of 7 a side. If the ball is on that side, I'll pass, shoot, cross with it. I'd easily take a penalty with it. I don't understand why so many players in the modern era are so one footed when their life is dedicated to improving as a footballer. Most people are born with a dominating hand and foot, but the weaker hand and foot can be strengthened. It just takes practice.