Personally, I agree with you, Twitter is very much like an economy... currently, some much of the Supply (publishing) is being manufactured, it's exceeding Demand, so now the Demand (real human readership) has to be manufactured with more bots... Vicious cycle. All this results in a bad experience for the average user. Twitter is a fantastic platform, it just has certain qualities that are now becoming more of a problem than before.
As for immediate automatic termination for thousands of messages per day - that's a gray area, because Automation (IFTTT etc).
There are also people making living off Twitter, some of the top "influencers" or "internet marketers" post hundreds times a day. You look at someone like Marc Andreessen (I can't see @pmarca, he blocked me on Twitter:)), his total tweet count is approaching 50,000 - some may argue even this isn't possible for a typical person with a job. He pulls it off though.
Going back to the topic of bots: thousands of messages per day is extreme, and that's not what most smart bots do. The biggest effect is resulting from ones that have learned to live and act well within Twitter guidelines, which doesn't just make them harder to detect, it makes them harder to ban.
Here's a random account, it posts a million times a year, or 2,700 times per day:
