I don't think Shaq helps that much. We already have 3 very good big men, and we'll have a 4th at some point.
Is only having 3 solid big men for the first half of the year going to result in too many minutes for KG and JO? What if Perk has a setback in his rehab? Let's say Perk does return strong, he still is a non-factor offensively and won't be able to take advantage of Miami's Center by Committee as well as Shaq would. Having Perk, and a potentially not 100% Perk at that, would allow the Heat to play us much more honest on D.
Basketball is a game of matchups and ur biggest threats to #18 are as follows:
Orlando. Shaq isn't as good defensively as Perk is on Howard, but he is big enough to not allow good post position and could draw some fouls from Howard.
Miami. There Center by Committee looks to be between Big Z, Magloire, Haslem, Anthony, and Juwan Howard. How many of those players could Perk take advantage of in the post? How many of those players could Shaq take advantage of in the post? Is Perk's better defense than Shaq really necessary vs. any of those players?
LA Lakers. They often play Gasol at the 4 when Odom replaces Bynum. Gasol was able to do this because Perk is a non-factor offensively. However, if we have Shaq the Lakers simply won't have the luxury of doing that and if they do they seriously risk having Shaq get Gasol in foul problems.