I thought it would be an interesting option. It would make an added dimension to space warfare.
My thoughts are that stealth would work much like scanning but with half the range. Reducing your enemies scanning directed at you by half a level for every level of stealth you have.
You would be able to turn off stealth with players of your choice. Stealth is automatically on, however you can turn it off on a players home screen with the click of a button.
Effect in Dark Galaxies: For every two levels of stealth it cuts off 1 level of scanning directed toward you. So if you have a star that would normally require your enemy to have scanning level 5 to see but you have stealth 5. It would reduce your enemies scanning directed at you by 2 and a half levels (5 half levels). So in order your enemy to see that star or any carriers traveling within the stealthed area they would need scanning 7 or 8 to see them.
Effect in non-Dark Galaxies: same as above but it would just look like a star out of range of your scanning.
Because Stealth is half that of scanning, in a race between stealth and scanning, scanning would always win. Enemy Scanning is at 20 your Stealth is at 20 thus making the enemies effective scanning is at 10.
In other words you can only hide for so long.
A couple mock ups of what turning on / off stealth would look like