I was interested in the question of the title and compared the prices of the account-wide upgrade with the prices of the infusions. Here are my results:
* We are only interested in Infusions with Attributes
* We want to reach 150AR but not more
* We freely select infusions (this is an important point, because you likely have a lot of +9 infusions but you can't downgrade them into 2 * +7)
* At 25 extra AR you need no +9 infusion anymore, I stopped calculation here
* Comparison of "normal" +9 infusions and Integrated Fractal Matricies (feel free to calculate the gold-price of them)
* Fractal relics and Fractal journals are not taken into account
* We want to be as cheap as possible
* We are not interested in extra rewards like titles, etc.
As a result of the last 2 points we are generally take Agony Impedance over Mist Attunment
* If you only have one character with +9AR/+7AR +5Attribute infusions then Agony Impedance I +II is ok for you
* If you have 2 characters then Agony Impedance III + IV is getting interesting, you still need to pay more normal +9 infusions, but you safe Integrated Fractal Matricies. This stays the same for 3 chars
* If you have 4 characters Mist attunement I is getting interesting, you still pay more +9 infusions but safe some Integrated Fractal Matricies
I hope this help some of you deciding wether or not buying this new upgrades. If you find any bug or have a better solution feel free to post it here.
For detailed information take a look at my excel sheet (the labels are in German sorry for that):