This is the type of stuff I think of. I think of these little things that would be so cool and creative. Sadly developers wouldn't even glance at my ideas or anyone's for that matter. Policy. I think if developers just took SOME ideas from fans they could really do some cool shit.
The last developer I'm aware of that did take suggestions from the fans actually asked a few magazines in the UK to get the reader opinions on what they wanted to see in the game - and a lot of the suggestions got included in the game itself. The developer was Rareware - and the game in question was Perfect Dark on the N64. (Note : By far the most common request was for mines to stick to the characters rather than bouncing off like they did in Goldeneye...)
Anyway, on topic, the spray paint is the worst "weapon". I do disagree with the itching powder view as combined with stink bombs they can produce some hilarious riots...