We built two robots. Between the time the first one is (mostly) complete and tested and the first bagging we build the second one. This allows us not only to refine the mechanics, but gives software more time to develop, and plenty of time for the drivers to practice as well.
Having spoken with a mentor of the HOT team (67) just before St. Louis 2011, they do this as well (2 robots, 2 languages). If memory serves, the main team featured in The New Cool also builds a second robot, though only one programming language is used. (That season anyway)
Again, this depends a lot on resources. Both students, mentors, and of course, funds.