You say you don't want to see Hamilton as your Center Fielder. Then why would you want Dunn on the team because Hamilton will play CF if Dunn is on this team? Griffey's not going anywhere next year and probably not the year after that.
The only way to get Hamilton out of CF is to get Dunn out of Cincinnati. Bruce will be the CF by sometime in June of next year if his current .947 OPS holds up in AAA.
Junior may not cause you to attend a game, but he causes others to attend a game. He's worth a huge dollar amount to the franchise both in credibility, marketing value, and attendance. People love to see Ken Griffey, Jr. play baseball, and he's playing fantastic this year. An exceptional human being who has several good years left in him.
You're trying to justify signing Dunn because it's only a $3M raise. Actually it's only a $2M raise. $13M - $10.5M - $.5M option buyout they don't have to pick up. But, it could be up to a $5M raise as bonuses kick in for 2008 that could push his deal to $16M.
But the ONLY'S don't stop there. In 2007, it was ONLY a $3M raise ($10.5M - $7.5M). In 2006, it was ONLY a $2.9M raise ($7.5M - $4.6M). In 2005, it was ONLY a $4.155M raise ($4.6M - $.445M).
So, for Dunn, he's had raises in the last three years of $3M, $2.9M, and $4.155M, and you want to give him another $2M - $5M when you have a guy who could step in and replace him adequately, superiorly on defense improving the pitching staff overall, much better hitting in the clutch, a legitimate #4 hitter (though as you pointed out, Dunn was always used wrong and I agree with you as he should have batted in the #2 hole and he would have been a 120 run scorer, hit for much better average for many reasons, and still gotten his 100 RBI's every year), hit for a higher average, but hit for less power.
Bruce won't be as good as Dunn next year overall, but Bruce will certainly be good enough to justify saving $13M-$16M.
No G.M. worth a grain of salt with the situation he has with the REDS would keep Dunn through the end of 2008 without a diehard attempt to trade him by the end of June so Bruce could take his place.
Your way would guarantee to keep the seats empty in the GAB as the REDS would have not enough monies to spend on pitching ensuring the club to flounder in the bottom half of the standings in the National League.