I like it too, but was always a problem for me:

> Customer collaboration -- over contract negotiation

Customer is often too busy with his own work to collaborate meaningfully.

If you go to the customer and the customer doesn't answer your questions, that is obviously a huge problem. Then that customer is not ready to work agile. Maybe the situation can be salvaged, maybe not. If not, then apparently it is not the customer you would want as an agile team.

If the customer doesn't think their project is important, why should I?

The manifesto intended that your customer can (and often will) be a proxy. You need a PM who gets out of the office, empathizes and understands clients, talks to customers. A big part of what's wrong with "agile" today is BS product managers.