You're overselling the point. Over the last 4 years LaRoche has actually been consistently solid. He's not Mark Teixeira, but then, who is? He is, however, likely to be available for trade and stands a good chance of being more useful than Kotsay. He's also at about the same level of production as a healthy Mike Lowell.
If that's the perception of LaRoche, then he's seriously underrated. Adam LaRoche is exactly the kind of 1B you get in the middle of the season if you happen to need one. Only, he's actually that guy, rather than the 5-10 people around the league that you could get hoping they're that guy like Kevin Millar or Chris Shelton. He's a legitimate middle of the order bat, gets on base reasonably well, and he'll give you somewhere between 20 and 30 HR's. And he'd probably be good for more than his traditional 90 RBI's if he ever played for a team that actually got on base sometimes.
As for Bowden being highway robbery in trade... ha. Talk about overvaluing prospects. Until he shows what he's got over an extended stay in the majors, he's probably worth less than a battle-tested Delcarmen.
I'm very high on Bowden myself, but he has proven exactly nothing and I don't think the team would hesitate to deal him for a piece that would help them win now and next year. And LaRoche looks like a legitimate possibility to be that guy.