Nelson is a fine player and someone most teams would want, but for Orlando's specific situation, bringing him back wasn't the right move.
First of all, Nelson is 30 years old. If the Magic were legitimate contenders, he would be worth the money, but they aren't.
Sooner or later the Magic are going to trade Dwight Howard, which means they will be rebuilding in the near future. Why give a new contract to a player in his 30s when you're trying to rebuild?
The Magic have spent the last half-decade in salary cap hell. At various times they've had several players with legitimate arguments for the worst contract in the league (Gilbert Arenas, Hedo Turkoglu and Rashard Lewis).
Managing your limited resources is very important to small-market teams. With that being the case, why should the Magic spend their money on Nelson?
As odd as this sounds, the fact that Nelson is a solid player actually works against Orlando. If they trade Dwight Howard and start rebuilding, they'll probably want to do it through the draft.
Having good players on your team doesn't help you get good draft picks. As we've seen with teams like Houston and Indiana, it's nearly impossible to rebuild while maintaining the infrastructure of the team you want to break apart.
Generally, it's all or nothing. When the Thunder (then Sonics) rebuilt, they let Rashard Lewis walk and traded Ray Allen. Not only did the Allen trade get them a top-five pick (Jeff Green), it also put them in a position to be bad enough to draft Russell Westbrook the next year.
That's the philosophy the Magic should be embracing. They should use Dwight Howard as a chip to completely tear apart the team and start over. Giving away big contracts to players from the soon-to-be expired Dwight era doesn't seem like a good way to do that.
Jameer Nelson is worth big money to some teams, but not the Magic. Orlando should have let him walk away.