Even if they got reallly lucky and still ended up with a top 5 pick next year, they'd be another few seasons away from being competitive with that group.
By that time, Bosh is in his early 30s.
Any way you cut it, even a weak #4 pick makes more sense for the Bobcats than Bosh because that player will still be contributing for them 5-6 years from now.
In any case, you really think Bosh is going to put forth any kind of effort on the Bobcats after playing in Miami the last couple of years? Much more likely he pulls a Ben Gordon.