It's not enough, because all announcements are bolded and displayed as shown by yourself, so eventually you just get used to 'that bolded bit at the top of your screen' and might not realise the change. I've missed a few announcements myself. The "pop ups" would only be for major announcements such as hackings (Amlyle's for example) or security information (SwiftKit incident for example) and could potentially prevent some scams or hackings here or there which in turn would prevent Sythe scams/hackings.
It wouldn't take up much time to click out of the pop up. When you dismiss a PM it literally takes 2 seconds, and at least you then know it's there, you can check it when you feel like it, if you choose to check it at all. A disable option for a one second click isn't really necessary/not a problem in the first place.