Dunn does score a crapload of runs. I think that with him it's a black-and-white matter of what categories you need help in, because he's great for homers and runs scored, but his average is just terrible. I traded him straight-up for Carlos Zambrano a while back and I'm expecting my team BA to rise just by him being gone.
The strikeouts don't necessarily count against your stats, but he Ks on a lot of called third strikes that he just chooses not to swing at. If he could be convinced to swing and make contact instead of striking out looking his value would be higher since he'd be getting more hits, but as is he'd rather just go for homers or nothing. He's a weird player with big payoffs and big drawbacks.