People who have no status on the Marco Polo Club, be warned that it is twice if not thrice as hard to get into an elite level if you're (sorry) a nobody at Cathay now.
In order to get Marco Polo Silver, you need to accrue 40,000 miles. Once reaching that goal, your loyalty miles will zero down to zero (but your award miles remain as they are in AsiaMiles). Then from there, you'd need another 60K to reach Gold (1w-Sapphire), which means you'd have reached 100K already. You'd get Exec Plat on AA for that. Then if you're crazy enough (like me sometimes), you'd try to get another 120K to attain Diamond. Which means, it is almost impossible , well, very hard for someone starting out to try and reach Diamond in their first year. You'd have to get at least 220,000 miles to get Diamond.
Perks are varied. Unless you live in Asia or travel to Asia alot, it's not really worth it. Economy class seats are guaranteed on any fare types within 72 hours of booking for Gold members, and both economy and business class seat guarantee for Diamond members within 24 hours of booking.
Diamond members can request for an upgrade to the next class based on avaialability or sometimes they just get upgraded.
But there are no tier bonuses.
I try and get Gold every year, as it's not really that hard to maintain 60K a year as I only like the guaranteed economy seat availability. But I'm going for Exec Plat on AA this year.