I rode most of the route yesterday: from the start as far as Chearsley.
At Chinnor, I went past "The Wee Bookshop" which is a bookshop/cafe that has decent write-ups. I didn't stop but I noticed that it had a couple of bikes parked up outside which is a good sign!
At Thame, per Dogtrousers comments, I varied my route by going down the Cornmarket (i.e. the High Street). It was closed to traffic due to a music festival, which wasn't a problem as I hopped off the bike and walked it, giving me time to spot cafe options. The James Figg is still very much alive and kicking. Further west along the Cornmarket is Treacles Tea Rooms, which conveniently had some bike parking opposite.
After Chearsley, I ventured up to Brill before heading east via Quainton and resuming this planned route into Oving. Such is my lack of miles in the legs at the moment, I was pretty tired by the time I got home - being blasted by the sun didn't help much. At least the planned route is shorter.