Bob Langill works in a mainframe shop, supporting legacy batch & CICS systems. There are those who would liken this to being a veterinarian for dinosaurs. 

My response "Maybe, maybe not. At any rate, I keep them in good health and performing their business"

The technical work environment I work with: the languages, operating systems, and application frameworks; they don't promote the full set of XP/Agile practices. On the other hand, the people I work with are good people I enjoy working with. Maybe I'm just lucky in that regard, but most of my career I've had good work relationships with people who appreciated what I did for them. And, even in my musty, old mainframe technology I still discover new tools and techniques for getting things done.

I believe that practicing the full suite of XP practices is one of the best ways to deliver value to clients. But, even short of that there are benefits to be found to using as much as you can.

I have two, what I call, XP Policies that help me keep focused and able to deliver:

1. Clients determine the value of what's been done.
2. The quicker I can deliver something they can check and use, the easier it is for them to keep things moving.   
 
Here's a short example that demonstrates how this has worked: 

Much of the client interface for our financial system runs through CICS. For those who aren't familiar, this means an 80 column by 24 line green screen. A business analyst and I were discussing problem with the way a few odd history items displayed. Our client, aware of the extent and nature of the problem, didn't feel it was worth devoting time to fix. But, as he was discussing this, he mentioned that it was a bit of nuisance that people had to page forward most of the time when they brought up an account with history. It was more of side remark than a actual request, but I recognized the opportunity to exercise some agility. With only a small change, the application could display the last page initially, but navigation would be unchanged. I wrote up this idea, tagged it as medium priority and posted it for client review. They made it a request and asked to have it worked right away. This was a small change, more time was required for testing than making the change. But as a low cost, low risk,  modification with quick deployment, it was loudly appreciated. What I did, didn't required a wizardly coding; all I had to do was listen and act.