Are all your ratings JAR-FCL?
CPL with B737 Type Rating and IR should suffice - if you are then offered further employment with another airline flying the A320, your A320 Type rating training would also include revalidating your IR on the A320.
The MEP Class rating only entitles you to fly MEP Class aeroplanes; you probably only needed it in the first place during training as a ME IR is required to open certain licences. I see no point in revalidating or renewing a MEP Class Rating unless you wish to fly such aeroplanes in addition to your airline's Type.