For Tough Hide - see this thread for an interesting discussion of Tough Hide and armor stacking.
http://www.ironcrown.com/ICEforums/index.php?topic=7112.0
As for negatives to make it less attractive - why is the character's skin "tough hide"? Does that have a roleplaying impact in dealing with others? Obviously in Spelljammer where varied races run amok, there is no negative so be prepared to have them take it. Of course, you can use the Monster Ability - not available for characters response, but as I have stated before I like to keep the door open on that, especially in a setting where most of the races are somewhat "monstrous" to begin with.
As for Giantism - the easiest negative impact is size related. I played in a spelljammer campaign where one of the characters played some kind of giant. Every time he wanted to have his character sleep he had to sleep topside on the deck of the ship because he could not fit through the doorways.