My first case of rough idle was a crack in the intake boot that would open up when I made a turn. The second case was a bad sparkplug coil and the third case of rough idle was a bad DISA valve. I'd be surprised if a sticking VANOS would be the issue considering your oil change habits. I've never had a VANOS problem and I stayed with the BMW Castrol and 7500-8000 mile change intervals.

2002 X5 3.0 298,000 miles
2014 428i 16,900 miles

2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles