I received an upgrade to Platinum in the mail from Mercury. Should I upgrade?

Here are the details:

1) Purchased 3/10/2010
2) I receive 3 years of platinum coverage
3) Then I receive two years of gold coverage (expiration 3/10/2015
4) I can upgrade the two years of gold coverage to platinum for $506.40
5) The difference between gold and platinum coverage is electrical and ??

Looking for some feedback, should I purchase the upgrade.
Thank you!!