It really depends on how often you fly and I would say you should definitely join if you can at achieve Gold, since most Silver benefits are included in Business class.

OW Ruby (MPC Silver) benefits:
-Access to Business Class priority check-in
-Access to preferred or pre-reserved seating (where offered)
-Priority on waitlists and when on standby (where offered)
-**(CX/KA only) Access to CX lounges when flying in Economy on CX/KA

OW Sapphire (MPC Gold) benefits:
-Access to priority Business Class check-in
-Priority boarding
-Access to preferred or pre-reserved seating when offered by the airline operating the flight
-Priority standby and waitlisting (where offered)
-Access to more than 650 airport lounges (with one guest) when travelling internationally, including premium Business Class and frequent flyer lounges, regardless of the class of service flown that day.

OW Emerald benefits:
-All benefits above + FIRST CLASS lounges.

*info from OW website

Asiamiles can be used to upgrade on AA&BA without being a MPC member.