Depends on the benefits you seek. If you fly primarily out of smaller market cities where you are likely to be upgraded as a PM, then stay a PM and use the rollover toward status next year. If you're border line and flying out of ATL as you're home airport, it's worth it reach DM as that significantly increases your upgrade potential. However, as others have pointed out, if domestic upgrades aren't important and you're only interested in the other benefits of being elite plus, then they're the same from PM to DM with the exception of the SC access. This then becomes a very individualized answer as to whether or not it's worth it to hit DM for 1 year or have status for 2 years at a lower tier.