Point to point DIYs are OK, and positively encouraged. I do them quite a lot, then jump on a train home.
One of my fave DIYs last year was a DIY 600 overnight to London Euston. I then jumped straight on a train to Manchester, and another home to Tod.
In fact, right now, I'm on a 730km DIY dart/arrow, from London to Edinburgh, in a cafe near Middleton Tyas.
If you're in South Wales or the West Country, drop IanH a line for more info. If you're in mid/North Wales or the Midlands, write to me.