There is no exact answer for this question but i could share my experiences.
One thing, You should update your farm to SP1, because you are on RTM version and MSFT release March PU which is mandatory for RTM version, But as of now we have the SP1 so you should apply the SP1 to all your farm.
I would never install any new released C until it really fix any bug which we are facing in our farm. We always Focus on the SP. Applying every CU is not a good idea because:
- its required down time and you dont want downtime every other month
- Also required testing again required alot of time
- Some time CU /SP breaks the things which you dont want.
There is one rule of thumb is Test you environment after applying the CU/SP1. As you have Dev, Staging and production so You should do this way. You should write some test cases as per requirement of your environment i.e if you using workflow so some test case for it, site creation, alerts, any EE services include those as well.
Here the steps we always followed.
- Apply the Updates to Dev then Test, Test and test
- Apply the updates to Staging farm then Test, Test and Test.
- Now schedule a downtime for your production farm
- Apply the CU to Production and test it.