You answered your own question above, and also identified why app.net won't interest you. If you're okay with ads, then I think you'd get zero utility from app.net
If even Google is having trouble getting traction with a social networking product, I don't see why anyone is confident that a social network users have to pay for will end up with a large enough user base to be useful.
Maybe App.net will nicely take care of that. I would definitely like to see a social network that provides me with content I want for once. Google+ has come pretty close, but that'll rapidly change if it gains mainstream traction, although Circles could prove to be a solution.
I unfollow people on Twitter when I don't care to see what they're posting. Most people don't use the tools that notify users when people unfollow them, so it's not a big deal. Even for the ones that notice, I just don't care. I don't use Twitter for friends; I use it for interests. If you're not posting about my interests with an acceptable signal to noise ratio, you're unfollowed.
Using App.net to filter out people you don't want to hear from won't work unless you think the value of ones posts correlates with their propensity to pay. I doubt that's the case, and you're definitely going to filter out plenty of worthwhile content that people post on Twitter.
It seems to me that people want App.net to succeed regardless of the likelihood that it will solve their problems. This is a good position for App.net to be in, but I don't understand it.