It's important to reach for the stars. However, if you don't have a good rocket handy, or at least a reasonable plan to build one on the drawing board, people are just going to roll their eyes and keep walking. No one is going to waste their time on a goal that's clearly not achievable.
A reasonable stretch can invigorate us. Muscles get stronger by pushing just a little further than normal, and well considered goals work in much the same way. However, when the carrot at the end of the stick is too far away to reach, it can have the opposite effect. If management is expecting huge gains that simply aren't in line with the laws of physics, people will become disheartened. Assuming they'll be blamed for the failure and realizing that it's inevitable, they'll shrug their shoulders and adopt a, "what's the use in even trying" attitude.
Many years ago, I saw a band by the name of Shotgun playing at Mother Blues, one of the top rock bars in Dallas, Texas. The bands there were always good, but given that the clientele were likely to show up stoned out of their minds, you needed a little something extra. Shotgun kicked off the first song, and in the second measure there was a double barreled blast of flame, smoke and explosions loud enough to carry over a blaring band. If you were there, chances were good that by the third measure you were quite alert and sitting up straight.
You want your people to do more than nod their heads and agree to follow orders. You want adrenaline. While I'd advise against explosions in the meeting hall, you'll nonetheless need some verbal pyrotechnics if you want to fire them up.
Once you do, show them why they should care. Then show them how it's not as much of a stretch as they might have thought. Give examples where possible to make it concrete and real to them. When people believe your goals are achievable, they'll not only put their shoulders into the work, they'll do so with great enthusiasm.