In general I take the fact that complicated data structures start to occur in code as a sign that it's time to introduce some classes (refactoring term: the code smells ;-) Usually the structure actually reflects the relationships between various objects (that can contain other objects, etc.).
Regardless whether or not this results in a speed up of the code, introducing OO definitely leads to clearer and cleaner code.
Just my 2 cents, -gjb-
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