Attendance is a question of wins and losses.  Everything else is a lesser factor.
		
		
	 
If you take out NE, IA and WI games, pretty much. Must have been one hell of a promotion for that NW game in 2000. 
I'd guess around 41,000 for Saturday. Here are the largest and average attendances for the last 20 years. It's from Gophersports.com. Looks like they didn't mention the 3,000 temporary seats for the two Vikings seasons. 
Metrodome Attendance
Capacity: 62,218 (1982-90) / 64,172 (1991-2008)
Year	Att.	Gm.	Largest Crowd	Avg.
1996	261,113	6	Iowa (53,349)	43,519
1997	269,385	6	Wisconsin (57,563)	44,898
1998	249,854	6	Iowa (50,640)	41,642
1999	318,086	7	Wisconsin (63,108)	45,441
2000	284,112	6	Northwestern (59,004)	47,352
2001	260,912	6	Wisconsin (55,890)	43,485
2002	292,492	7	Iowa (65,184)	41,785
2003	309,038	7	Michigan (62,374)	44,148
2004	285,438	6	Iowa (64,719)	47,573
2005	294,147	6	Wisconsin (65,089)	49,024
2006	313,239	6	Iowa (64,140)	52,206
2007	362,538	7	North Dakota State (63,088)	51,791
2008	342,705	7	Iowa (64,071)	48,958
http://www.gophersports.com/sports/m-footbl/spec-rel/attendance-records.html
 	 	 	 	 
TCF Bank Stadium Attendance
Capacity: 50,805 (2009-pres.)
Year	Att.	Gm.	Largest Crowd	Avg.
2009	355,635	7	Seven Tied (50,805)	50,805
2010	346,593	7	Iowa (50,805)	49,513
2011	333,996	7	Miami (Ohio) (49,950)	47,714
2012	326,456	7	Syracuse (50,805)	46,637
2013	334,581	7	Wisconsin (53,090)	47,797
2014	335,056	7	Purdue (51,241)	47,865
2015	366,484	7	TCU (54,147)	52,355