There have been 105 FBS conference championship games, 33 of which were rematches of games played earlier in the season. In only 5 cases were the games played at the same venue, since most CCGs have been at neutral venues.
C-USA, 2007, Tulsa at UCF: 10/20 (UCF 44-32, att 45510) and 12/1 (UCF 44-25, att 44128)
C-USA, 2012, UCF at Tulsa: 11/17 (Tulsa 23-21, att 19725) and 12/1 (Tulsa 33-27, att 17635)
MAC, 2000, WMU at Marshall: 10/5 (WMU 30-10, att 27109) and 12/2 (Marshall 19-14, att 24816)
MWC, 2014, Fresno at Boise: 10/17 (Boise 37-27, att 35008) and 12/6 (Boise 28-14, att 26101)
MWC, 2016, SDSU at Wyoming: 11/19 (Wyoming 34-33, att 19112) and 12/3 (SDSU 27-24, att 24001)
The first three listed had marginal drops in attendance, the fourth had a huge drop, and the fifth had a significant increase. Weather may have been more of factor in the difference than the fact that the games were rematches.
Only one rematch actually occurred in consecutive games (Stanford/UCLA 2012), but the venues were split, so you can't really compare attendance.
Here's a
list of all rematches. If anybody can find Nielsen data for these games, that might be more informative.