I like the idea of invisibility but not really for this certain situation, I would like it for Events, and when Invisible, I think people should walk threw you also.
For Events, you could use this to find teamers, hiders, and healers(in battle, I read some of your rules.). But for abuse reasons should only be enabled for Deathmatch. The invisibility with harassment, would kinda be abused, and could lead to invasion of privacy, i.e. maybe a Boy, and a G.I.R.L.(Guy in real life) are talking to each other, and a invisible ET listens to the whole conversation for their enjoyment. (For you dirty minded people, its a regular conversation, and for hypothetical purposes lets say its about, what they did last Thursday on thanksgiving.)