I would say that the stalkers are never worth their points. If they also had an additional CC attack, it would be worth it. Also, I always forget to make their shots at the higher BS. So, I never take them. I usually play 3k-3.5k games. In games that size, I will take at least 2 units of chameleons. I will try to get 10, or at least 7 in each unit. I will follow that up with either a unit of Terradons or another unit of chameleons.
As far as deployment goes, I routinely play a Brettonia player that usually denies me any meaningful deployement of my scouts. That said, I usually just deploy 12 inches in front of my targets. This works most of the time.