Different levels still doesn't work when changing your password. If twitter made me change my password, it wouldn't increase or decrease on my level of importance scale.
The idea is to have one password, with a salt(or service name) for all services. To make it a little more secure, you could set up different levels - email and social, news sites, games..., basically any way you want to do it, and have a different passphrase for each level.
When changing passwords, you just need to change the salt of that particular service.
