I am of the opinion that we should wait at least 5+ years before even thinking about expansion.
My criteria for expansion at that time would be: if the Gophers are consistenly selling out our least attended conference game and at least 47,000 seats to our least attended overall game, then we can talk about expansion.
As reference, those numbers (least attended BT game and least attended ooc game) are as follows:
2008: Indiana (40,511), Florida Atlantic (41,003)
2007: Illinois (46,604), Miami of Ohio (45,383)
2006: Indiana (44,610), Kent State (45,612)
2005: Michigan St. (45,187), Colo. State (40,221)
2004: Northwestern (44,657) we were ranked #18 for goodness sake, Ill. St. (34,006)
2003: Michigan St. (38,778), Troy St (31,093)
2002: Illinois (32,663), SW Texas St (32,209)
When we have 5+ years of a packed house, ask the question again and then I will get into how much we can expand. For now, lets be "tremendously excited" over what we have.