Low CPU Utilization but High Signal Waits
Community Wiki answer generated from comments on the question by Aaron.

Unless you are having performance issues, the high percentage of CXPACKET waits may only be an indicator that a large portion of the queries are going parallel and not actually a problem.


What is the CXPACKET wait type and how do you reduce it? 


High CPU could be a indicator, but from what you have explained I would say look at queries with long durations but low CPU to start with. The CXPACKET wait is sometimes associated with a query waiting for all of the threads to finish before it can merge the results (data skew).

If you are able to modify the queries and procedures, you could set a higher MAXDOP for the warehouse tasks that need it, and set the global MAXDOP lower. However, I would only do that as a last resort. You only really want to make those types of explicit hints when you've exhausted all of the possibilities or you can't make changes to the code, queries or database schemas.