Okay, I found some of it at least. Here is the recent history for our home opener:
2008 - SDSU - Thursday - 46,617
2007 - Kent State - Thursday - 47,313
2006 - Toledo - Thursday - 42,531
2005 - Illinois State - Saturday - 44,058
2004 - UNI - Saturday - ?
2003 - UNI - Saturday - ?
2002 - KU - Saturday - 40,026
I haven't managed to find our numbers for the UNI games in 03 and 04, but those may skew higher just because we always have great attendance for UNI. Looking at the other games, I would say we have actually done a little better on Thursdays.
the key numbers are not the sales for the individual days, but you have to compare them to the average attendance for that season (to try and remove other factors such as season ticket sales). Look up the 'thoughts on thursday night game' thread from earlier today and i posted all those numbers.