Ha ha, impeded airflow! One of my coworkers had actual numbers for MTTR (Mean Time To Repair/Reconfigure/Replace) and MCTR ('Cost' instead of 'Time') for tight racks vs. slack racks (after a merger of two companies with vastly different cultures) and the numbers aren't supporting the claims of the OCD crowd.
I however understand your position when marketing yourself to the owners of Spondoolies' hardware which is in large part "status symbol" crowd.
I just went and measured. In the wake of the mess of power cables, airflow is around 2.3 m/s. In a similar position above, not in cable wake, airflow is about 3.8 m/s. If you feel around with your hand, the effect is quite distinct. There is no noticeable effect from ethernet cables, though.
The performance and reliability of most servers is not significantly affected by airflow resistance. If a server gets a little bit too hot, it increases the fan speed. With SP30s, the fans are running full blast anyway, and the performance is affected by internal temperature. I would think that this would be a bit more sensitive than MTTR/MCTR for some 10 kW racks.