Hi Echo,
You're in a very competitive space, so I would say I'd focus more on getting quality unstructured citations. One or two from colleges and universities or government organizations could indeed tip the balance in your case. Have you thought about giving free rides from O'Hare and Midway to incoming guest speakers at various seminars / colloquia @ Univ of Chicago, Northwestern, etc, just as an example?
Taking a quick look (assuming this is you) -- I'd suggest trying a couple things first, though:
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set your service radius much tighter (something like 30 miles)
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get more reviews on TripAdvisor, WeddingWire, AngiesList, and Yelp. These seem to be the most prominent review portals in your space.
Hope that's helpful.