As an experiment, count up the number of distinct people (that're following you back) that you've had twitter conversations with in the past 60 days.
The tweet-per-day rates for these accounts roughly follow a power law, going by a mix of sampling individual accounts and observing my own TL. A decent number are known to be real but look essentially abandoned(from a follower's perspective - they may be lurking). At the other end some top 200 tweets per day. The middle of the curve is at around 4-5 TPD.
These accounts do not all treat Twitter uniformly, of course. Some broadcast their personal updates to work or life. Some of them ask questions. Some are posting bon mots. By far the most popular activity is commentary on news items, though. Because I follow so many accounts I also see a substantial subset of semi-private conversations, which usually appear from the commentary tweets.
Now: Is this valuable? The technical restrictions mean it doesn't replace email or regular blogging, but I see a lot of serendipitous conversations that can't occur in other contexts(too much overhead). This is nearly ideal for creative types, and I believe that is what's making them gravitate to it.
and
many have replaced it with texting.
Non sequitur. Your facts are uncoordinated.