I'd replace the nitrogon with a big shuriken 2 or something in that range.
I second that. Also make sure whatever you get has the appropriate mountings for the current AMD system as well as Socket 1155 and you can keep it.
I dont see that you would need to replace your case unless you add a high-power graphics card, just your CPU cooler, or perhaps just change the CPU fan control - there is a very real chance that its "over-cooling" and could be turned down a notch without reducing stability.
Also, make sure that there is adequate ventilation for all incoming and outgoing vents and that you should really have a second case fan if you dont already as the airflow in the case can be very easily impeded due to its unusual layout (e.g. not a straight through airflow design).