It depends on what do you want from the upgrade.
I usually don't update production systems, if I don't have a reason to.
If I need some new feature (64bit aggr,flash pool, etc.) I update to version in which this feature was introduced ( provided it doesn't have any significant bugs) and work my way up from there. Does it work? Fine, leave it! Some problems,bugs,unexpected behavior? Update to latest patch version.
If I am deploying new storage system for new customer I usually deploy the most recent version of DOT.
It really depends on what you are expecting, there is no definite answer. Some people will say that you should always update to the latest version, more conservative people will tell you to stick with the version that works and don't try your luck.
So bottom line: It's up to you