I always say to people that you shouldn't power up anything until you absolutely need it. We currently have no need for any fire types or do I see anymore reason in the near future.
Heatran's a great pokemon with great stats. It's movepool isn't optimal at the current moment making it perform worst than Moltres or Entei. Id advise that you stock up candies and such to use when it returns in the future with a better movepool.