I like the idea, so far it seems useless to attempt to use nebulas and asteroid fields for cover, or even hiding behind planets, which should have some effect in blocking a signature. If you manage to escape an enemy and get just enough distance, you could actually find a nice big rock to hide near, or go off plane, and power down until they have passed. if you are good enough, they may miss you, if not, you may get destroyed anyways, there is risk and advanatage in the action. Makes using your eyes necessar instead of just relying on the scanner. I seems like a simliar advantage to the cloak, but you can't be seen while cloaked, i assume you would still be visible while powered down, which would mean you must hide or risk being hit with your shields down, and now weapons or engine power. It would also make sense that your own scanner would also not function while powered down, so again, a good pilot would have to rely on his eyes. I think it would be quite interesting