I want to know how does that Gold challenge thing works. Is it only for non-gold members?

I got a thing in the mail today telling me to register for a bonus which will give me 2000 for just flying 1 one way flight between May 1 and July 31. Does anyone out there have the same offer. I think the gold challenge is a better deal.

Is there any Platinum Challenge?

Is there any way to get my bonus offer changed to a gold challenge?