You should get tested if it will aid in defining the DNA profile of your surname ancestors. When your DNA profile is combined with another descendant of a common ancestor, it can define the DNA profile of that earlier ancestor. When combined with your brother’s result, your test will define the common ancestor (your father). When combined with a 5th cousin’s DNA, your result will define the result of your gggg-grandfather.
For a man who has already had a close relative tested, there may be little value in his additional testing unless there are specific questions to be answered.
Of particular concern are the sole surviving male representatives of a family line. Once they are gone, their family cannot be directly represented. These men are particularly important to their family study and should be strongly considered for testing. Many families already have stories of DNA testing a family member who has since died, or of not getting a test on a family member before they passed on.