Oh certainly a huge yes regarding SP-release :exclamationmark:
Why, because IMHO a SP is considered to be a stable release, tested well by the manufacturer. Certainly worth a general test and go.
A cumulative update is just a new package of hotfixes, designed for certain issues, so IMO not _that_ stable for us (systems managers) to give it a general test and go.
Also with CUs the frequency is to high to set up a release cycle every time.
After all, we have to determine which version of the software we will install by default when a new instance is being asked for.
For now that is set to SQL2005 SP2 + CU4.
But the active production instances are not yet being upgraded with CU4. (they are still on CU2)