18-23 homers really aren't enough. He's never cleared 30 doubles, so if he's stuck around 20 home runs that's a recipe for a .150 ISO, which isn't enough for a major league first baseman.
I mean, I really could care less if he turns into a weaker fielding Casey Kotchman (a 10-year major league career as a second division starter is nothing to sneeze at) but that's not a player any club with hopes of contention should count on as a long-term solution at first base.