is Joe Smith really that good? We're talking about Joe Smith...
It's not only about Joe Smith's value in abstract... He's a good player, he'd easily be our best backup big and he's a good addition for any team, but his value is much increased for a team like Cleveland, post Ben Wallace's injury.
See it this way: Big Z struggles to play more than 25 mpg at a high level and he's basically deadweight if he's to play more than 30 minutes (and there's a good chance he becomes literally dead if he has to play more than 35). Anderson Varejão is a limited offensive player and, while good, not at Wallace's level defensively. KG will give him fits and if Varejão wants to keep his aggresivness he'll collect fouls at a faster rate he'd want to. I think that Z and AV can give Cleveland 65 quality minutes at most during a playoffs series. They still have 31 minutes to cover. LeBron at the 4 is a solution, but that would weaken their wings pretty much, especially considering that Pavlovic is also injured and history says he'll need a training camp to get back in game shape. So, you'd probably see a rotation of JJ Hickson - 20 minutes; LeBron - 10 minutes; Lorenzo Wright - 5 minutes. Hickson is a gifted player, but he's extremely raw, way more than Glenn Davis last season - he struggles defensively and he fails to box out, for example. It's questionable if Wright should still be playing basketball. Our bigs would destroy those guys, they would have a single player able to cover Garnett and even Powe. AV in early foul trouble would be a nightmare for Cleveland. James at the PF would imply a field day for our wings. We also have our weaknesses (for example, the lack of a legit backup wing), but not such a big one, I think. They'd be very vulnerable for a team like the C's and I think their chances of beating the Lakers would be merely theoreticall.
With Smith, you now have Joe Smith playing those 20, 25 minutes and JJ Hickson those 5 minutes when needed. An incredibly better situation - a big men rotation of Ilgauskas, Varejão, Smith and Hickson (plus LeBron) is pretty good. Big, big difference in my opinion.