I don't really go to Gadget more than once every four hours. Not sure why the utility is an issue. I love my transporter and keep it in my bag at all times. It is so much easier to just pop over to Gadget and help summon.

Getting to Tanaris isn't really an issue now that there is an instant teleport from Shattrath (providing you are revered with Keepers of Time). Utility is an issue because if something is of little practical use then what is the point of having it? You obviously feel differently but, to me, having the ability to teleport people to a single destination once every four hours (a destination that most people who have run the CoT instances a few times can easily get to themselves) isn't particularly amazing. I suppose it has some use for those that haven't reached revered with the Keepers of Time, but most people I know just use the instant teleport from Shattrath if they want to get to Tanaris.

You do realize that there will be other teleportation spots right? Right now there's a Gnomish spot in Blade's Edge and a Goblin spot in Netherstorm. I've used my teleporter quite a few times to get back to outland when my hearth was on cooldown. We already know there's a goblin town in Northrend and possibly a gnome one as well.
Besides, if wormholes give you a teleportation malfuntion, it will be more than worth it.