Saves are really hard to project, because so much of save totals for closers depends on luck of the draw related to how many save opps they get. A team that wins alot of games doesn't necessarily generate the most save opps, and vice versa (in 2002 Mike Williams saved something like 45 games for a Pirates team that won only like 70)
The reason why Gagne gets so many save opps is the combination of LA having a great rotation to shut the other team down and a terrible offense that rarely blows the other team out. Detroit has a weak offense like LA, but unfortunately they also have one of the worst pitching rotations in the league, so they will get lit up and blown out alot.
As far as Urbina's other numbers, expect a repeat of last year. He is going to the AL which hurts somewhat, but remember that he spent half of last year in the 2nd best hitters park in baseball, so the effects should neutralize.
As far as saves, I would predict around 25. Any higher than 30 is possible but highly unlikely.