Club Nintendo FAQ to the rescue!!
http://www.nintendo.com/consumer/club/en/faq.jsp

How can I reach Gold or Platinum status?
Gold or Platinum status is based on the number of Coins earned in a Club Nintendo year. Each Club Nintendo year begins on July 1 and ends on June 30. If you earn 300 Coins during a Club Nintendo year you will reach Gold status. Earn 600 Coins during a Club Nintendo year and reach Platinum status! If you are part of a Club Nintendo family account, the Coins that each family member earns are combined, so you have a better chance to reach Gold or Platinum status.

Club Nintendo members or family accounts that reach Gold or Platinum status by the end of the Club Nintendo year will become eligible to receive a special reward. Watch for an email and details on club.nintendo.com shortly after June 30 for an announcement of these special rewards. You will have a limited time to accept that you would like to receive this special reward.

Your status will reset annually on June 30.
Why are my Coins listed with an expiration date?
Unredeemed Coins will expire two (2) full Club Nintendo years (July 1 - June 30), plus whatever is left in the current Club Nintendo year, after they are earned. Example: Coins earned in March 2009 would not expire until June 30, 2011.

There's a simple solution to this. Don't register your games until there's something you want to get and you know you already have enough points available to you(based on how many eligible unregistered games you own).