Oh nice - I did the NDW100 this year and hadn't recce'd much of the course. It's a lovely trail though before and after the section within the M25. Hoping i can squeeze in the NDW50 next year, or the SDW50.
Yes, I live about 5 miles from Avebury so it's easy to get onto the Ridgeway. You're right, I'd only class it as "undulating" rather than hilly. Most of the hills you can run up without blowing up, but yeah I've heard the other end is much hillier. I'm hoping to get up to the Ivinghoe section in the next month or so (as long as the plantar fasciitis clears up quick!), if you want to recce a section on morning / afternoon.
Still haven't entered yet as I'm giving it a couple more days to make sure the foot heals first. I'm doing lots of cross training and, with the glorious weather we're having, I can't say I'm utterly devastated not to be running outside!!