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