changing the filter is definitely important. I would tend to side more with the guys changing filters more often than oil than changing oil more often that filters. All modern cars are equipt with a filter bypass system, so that if the filter becomes clogged the engine can maintain oil pressure. This means that if the oil is not easily passing through the filter some or all of it may be bypassing the filter, which - short of running without oil - is one of the worst things that can happen. If you do extend your oil changes, whether using synthetic or not, its probably still a good idea to change the filter at prescribed intervals. I am sure that given these modern oils that the filters probably loose efficiency before the oils will. I still like to change my oil more frequently than most, and I do believe that I will be rewarded in the long run.
1995 E420 - retired
1986 420SEL - retired