which one to attend as a spectator?

The one in Lincoln is KCBS the one in Springfield is not. I guess it depends on what you want to do.
Lincoln also has the Balloon fest going on at the airport. I believe a band playing Friday night at the airport. The BBQ contest is downtown on the square. Also on the square is a art and wine fair I believe. Just off the square a block south is a Craft/flea market going on. So a lot happening in Lincoln.

Now downtown Sprignfield has the BBQ and Blues festival going on. I think the music starts at 3:00 pm and goes until around 10. It does cost to get in. I think $10.00 per person.

Both places will have BBQ vendors setup so you can purchase BBQ. Which ever one you decide to go to check out Twyford's BBQ. They will have a vending trailer setup at both events.

Personally I will be at Lincoln judging Saturday but I think I will go over on Friday and visit with some of the teams.