So, a few days later.
My BD rips were playing fine, but my menu's on DVD's were not. A bit of checking told me one of the players did not support MPEG2 but playing with the settings only proved that one does not work and one worked badly.
I already knew that you needed a MPEG2 license for the Pi, but with Blu Ray playing I was loath to buy one until I had investigated. However, £2.40 later I installed my MPEG2 key and, voila, my DVD menus now work. The knock on is that my Blu Ray's are now a touch more flaky.
Effectively I have a fully functional media streaming box for £51. I already had a Logitech remote which is HF and so does not need line of sight. I've had to use it because my IR remote requires me to unplug the IR receiver and plug it in again every time I start it. I'm sure I could get a more compatible remote, but also, for £1.15 I can get an IR receiver and fix it to two of the pins on the board and glue it to the case. Then the remote would work perfectly with it.
I'm going to do some playing with a playlist generator this weekend but I think with a small amount more work, I will have a fully functional media streamer which I can let Mrs S lose on. If I were to add a DVB-S USB adapter to it, I could also do recording of programs to my server. Something for another time when I'm not so tired.... I could also add a USB external DVD player to it, but, honestly, I'm as happy with an additional unit which does iPlayer and Netflix.....