How can I monitor my server’s status before changing the “Cost threshold for parallelism” settings
If you have a lot of CXPACKET waits it is possible that reducing setting the MaxDOP is appropriate and will help. You should not change the cost threshold for parallelism setting assuming you have a NUMA machine (which you most likely do).

MaxDOP: https://support.microsoft.com/en-us/kb/2806535

...and I read somewhere that cost threshold needn't be changed but am still trying to track that link down :(

In any case, focus on MaxDOP.