i think i started doing this out of some vague uneasiness about return handling scalars or lists. now that i think about it, it's pretty much a personal style thing at this point. which do you think is more appropriate?
When in doubt, parenthesize. At the very least it will let some poor schmuck bounce on the % key in vi.
Even if you aren't in doubt, consider the mental welfare of the person who has to maintain the code after you, and who will probably put parentheses in the wrong place.
My rule of thumb is that if the syntax and meaning are perfectly clear without parenthesis, you can omit them. If leaving them out makes the code confusing, alters the outcome, or impedes readability, better include them.