It's ok.
I have never done it at Spamalot.
I have at Wicked and got row G. I went for the lotto, lost, and since my friend and I didn't go for the cheap tickets, just for seats, we hopped on the cancellation line (about 2 hrs before the show). Waited maybe an hour until we got tickets. The people after us waited maybe 20 mins after us. My friend and I were first in line.
FOAntic was behind us.
Of course, Spamalot's door is outside, to the right of the main door.