if he can put up the numbers to make himself a desirable draft pick, and his goal is to go to the nfl to make a bunch of money, then I think it is a wise decision to declare sooner rather than later (given that there isn't like an overloaded draft with good prospects)
if he doesn't get drafted, then it's not a smart decision
as far as the bowl game goes, I usually think it's foolish to sit out the bowl game (since it's arguably just-as if not more important than a regular out of conference matchup at the beginning of the year) - however, Iowa actually made the Big 10 title and lost so I would understand this more than a team that has no shot at the title mid-season and then the player decides to arbitrarily sit out the bowl game rather than the point where the team no longer has a shot at a conference championship