A nice feature to add into alerts would be delete all or the ability to only get a limited number of posts per person.
You can turn off notifications for those you follow or greatly adjust what notifications you get from them in the settings tab for alerts you want to receive. I only get new post alerts rather than comments, etc from those I follow and it cut the numbers down significantly. There is also a "delete all except the last week" option under the active notifications tab. I know it's not a delete all option but wanted to make sure you knew it was there.