Increase power of emitters on objects? Is there a way to change the power of an emitter hitting a certain object? For example, if I had an emitter object with strength 5, and nearby had several other objects, could I set one of those nearby objects to treat light rays hitting it as twice as powerful, so that it would be hit for strength 10 while leaving the emitter as strength 5 for the rest of the objects?
The closest thing I can think of is doubling the entire shader of the object you want to be more illuminated.  This is done by adding the shader to itself.  To do this plug plug your shader nodes into both sockets of an add shader at the very end of the node tree.



It produces the following result.  The center ball uses the above technique while the other two use just the node group.



The disadvantage of this is that it doubles all rays hitting the object, not just ones from a specific emitter.

See this post and this post for more on the add shader node.