The answer totally depends on the other factors: score, are we moving the ball with any success, what's the offensive trend.
For example, We're on their 30 after a 5 play 60 yard drive (started on our ten) and we're looking like we can move the ball with reasonable success...it's tempting to go. If we're down 2 scores...even more tempting. If we got the ball on their 30 after an interception, previous offensive possessions have been...well..offensive....kick for the points.
The bottom line...the farther behind you are, the more tempting. The more success you've had offensively, the more tempting. The closer the score and/or the more you've struggled offensively, the less tempting.
Also, a fake is always on the table.
In general, as a massive underdog, you probably need to play aggressively to make things happen. We really have nothing to lose tomorrow....play like it. The real question is this: How big of an underdog are we? The spread is just a representation of the betting public's opinion (or the Vegas oddsmakers thoughts on the betting public's opinion). We hung with the same team that they got lucky to beat, we're playing at home, and anything is possible. But our success vs PSU was with a better offensive line and a healthy Butler and Jewell.
Go back to 2012 against Nebraska. We sucked that year, nebby was pretty solid. We're within a score, late in the 4th, on their 32 with the wind and time running out. To me it was obviously our last shot to beat them. We were underdogs, had struggled offensively all game and were highly unlikely to get back into scoring position. We punted. While less impactful to the program than taking a knee vs tOSU in 09, it pissed me off more. Going for it there was a no brainer. The season was a total loss, no chance of a bowl, we literally had nothing to lose. Why in the hell do you punt it there even if it's a low percentage play?
This crap is always hard, especially with Iowa. We can suck vs Central Michigan and then beat a blueblood in the same season. Who knows?