About the stylistic note, Code Complete chapter 18.2 cites a study Program Indentation and Comprehensibility from 1983 which found that a 6 space indent resulted in lower comprehension than a 2 or 4 space indent did. But the same study reported that many of the people in the study self-evaluated the 6 space indent as being the easiest to read, even as they scored worse on it! (The same study found that an indent in the range 2-4 spaces was optimal. Which one you use doesn't matter, that you use one does.)

Your pair of 3-space indents amounts to a 6-space indent. Exactly the combination that had people's self-reporting about usability conflicting with their actual performance. In my books aesthetic judgements lose to performance every time!

Therefore I would suggest that you either change your overall layout style, or change from 3 characters at each step to 2.

Steve McConnell goes on in 18.4 to say why he thinks that a double-indentation style is a bad idea due to the fact that the resulting code winds up looking far more complex than it is. However the actual research he found didn't really show whether or not there was a large real difference. Therefore while I agree with him that you are making the mind process a large amount of irrelevant structure at a glance, I wouldn't say that item is nearly as important as making your overall indentation smaller.