1: Spider-tron is immune mainly due to performance reasons. Right now the most expensive thing that can be done in the game is something being cut apart. During play testing of the new levels the game would grind to a halt on low-medium end machines if Spidertron fell among the saw blades. Due to the level design, there is often nowhere for the body parts to go, so they get bounced around and get cut again and again. So it's really cool on high end machines, but not so cool on low end ones. A difficult balance.
2: Kicks are most likely going to be activated with the right mouse button. There'll be a standing kick, a jumping kick, a jetpack super fly kick, and if I ever add crouching: possibly some sort of circular leg sweep. That's my initial plan, but once I start implementing it it might break the game and need to be changed/adjusted. The standing one might just stagger rather than knock people over for example. It should be easier to kick than it is now, but not be without risk if you don't time it right. :)