The whole point of analogy problems is to test reasoning skills. Specifically, logical skills, inferences, categorization, and so forth. The vocabulary test nested within the analogy test is incidental. It creates a bivariate challenge (vocabulary + categorization), which is not necessarily an invalid test. It's just not a pure test of analogies, and it's also duplicative of the vocabulary portion of the test.
In re the value of analogies, there are some computer scientists and philosophers who believe analogy-drawing is the irreducible core of higher cognition. I'm not sure I'd go that far, but Douglas Hofstadter has come close:
http://www.amazon.com/Surfaces-Essences-Analogy-Fuel-Thinkin...