The only thing seperating Silva from being a below average pitcher is pure luck. When that averages out you are looking at an unappealing pitcher. Toss him in front of a team that is ill suited for Silva's game and you have a disaster.
Teams with great defenses may consider Silva a good gamble because they can stretch his skills to the max, the Reds can't do that. Instead find pitchers who control their own destiny (high walk, high K, low in play) that won't be hurt as much as because of the team around them. M2 mentioned Cabrera as a possibility yesterday (albeit as a reliever) but that's the type that won't be killed by defense. He's not a great pitcher, but his problems won't be compounded because of the defense.
Isn't his low BB rate a skill? He's suppressing HRs pretty well now, too, and that's in the AL. Also, the Reds defense is much improved with EdE playing well, Phillips at 2nd, and, by 09 at the latest, Griffey gone.
I think folks are underestimating the importance of having 6-7 guys who can start at the major league level. Silva gives you that solid 3rd guy, while Belisle, Bailey and Cueto, the only in-house options, remain question marks. So, you're at 5 -- without even acknowledging the possibility of injury.