I received an email from Club Nintendo as a reminder that the Club Nintendo year ends on June 30th, and it also says "If you achieve Gold or Platinum status by June 30th of this year, look out for a special thank-you gift from Nintendo before the end of the calendar year."
For anyone who still had doubts that Gold members get a prize, here is further conformation. It doesn't say anything about what that prize might be, but I'd be surprised if both membership statuses got the same prize; what would be the point of having the two different types then?
It also looks like you won't be able to claim that prize on July 1st, or possibly even July. By the end of the calendar year? How long is it going to take? We've impatient here!