Is CHO still having issues with its ILS? That could legitimately make it a "weather" cancellation; it seems like several CHO flights have gotten nixed of late for that reason.

However, I'd still press for some compensation--the rental car would be nice--and see what you can get. Since it was "mechanical" when it was cancelled, you should be able to get something... of course, knowing how out of it the average UX op is, I don't know that I'd trust anything from the original equipment swap story to the mechanical to the weather--UX often doesn't know one end from the other.