Are my kinematic rigidbodies slowing my scene down?

Why do you need so many rigidbodys? Think of it this way: The more objects you have idling, the slower it will be. If you're not doing any collision checking, then why have kinematic rigidbodys at all? (Yes, most of the time there is no difference in performance between very close, non colliding objects and colliding objects)

Thank you for the reply. The reason I have so many rigidbodys is because each can potentially be hit with a bullet, so the bullet needs to have something to collide with and react to.

The buildings/cars scroll past from right to left. At any one time, there are a maximum of maybe 20 in the game. I create them offscreen on the right, move them through the scene to the left, then destroy them when they're offscreen. I might try sleeping them as they are created, and setting a sleepVelocity as their current speed (which remains constant throughout their life). If they're hit by another kinematic rigidbody (i.e. a bullet or the player), that should wake them, correct? Would this help with game performance?

The other thing I have considered doing is not creating/destroying the gameObjects as they're needed - instead I would create everything at the start of the game and leave each object sitting idle until needed, resetting them once they've been used and effectively recycling them. Potentially helpful?

Thanks!

Well definitely avoid instantiating things when the game is playing - that's a killer on performance.

Perhaps its the performance of your collision handling code, could you post some?

You do know, that you do not need a rigidbody on both sides of the collision? From what I understand you just have a bunch of moving geometry and a bullet. Unless you want that geometry to affect physics (move things), there is no need for rigidbodys to be attached to it.
Always avoid Instantiating, but you should also use the profiler (in pro) or just the stats popup (in free) to see what is causing your performance drop.

Benproductions: You're right... I didn't realise that I didn't need a rigidbody on both sides of a collision. I got that notion from the Unity doco, which seems to say that if you're planning on moving an object, it needs both a collider and a rigidbody:

A Static Collider is a GameObject that has a Collider but not a Rigidbody. Static Colliders are used for level geometry which always stays at the same place and never moves around. snip

Static Colliders (without a rigidbody) should not be disabled, enabled or transformed. Altering these Static Colliders will cause an internal recomputation in PhysX that is quite expensive and which will result in a big drop in performance.

But after reading and re-reading, I think they're talking about objects under the control of the physics engine, and not objects that you can move around. I guess I got confused because they talk about static colliders right after kinematic rigid bodies (http://docs.unity3d.com/Documentation/Components/comp-DynamicsGroup.html)

So I will try removing the rigidbodies from everything except my bullets and see how that improves things. I will also alter the code to recycle the gameObjects rather than create/destroy.