Trying to take over the universe isn't utility-maximizing under many circumstances: if you have a small chance of succeeding, or if the battle to do so will destroy most of the resources

Obviously, if you can't take over the world, then trying is stupid. If you can (for example, if you're the first SAI to go foom) then it's a different story.

or if you discount the future at all (remember, computation speed increases as speed of light stays constant), or if your values require other independent agents.

Taking over the world does not require you to destroy all other life if that is contrary to your utility function. I'm not sure what you mean regarding future-discounting; if reorganizing the whole damn universe isn't worth it, then I doubt anything else will be in any case.