Thank you TalkBoard and starflyergold! Look at the results!
I firmly believe that it was right to start this forum, and it looks like the threads populating it below are the best testimony. Bravo, all around.
Now, although a member, staying rather frequently at airport Ibises - at the weekend! - I hadn't thoroughly perused all the aspects that starflyergold describes. (Thank you again!) Re the programme: Awfully labyrinthine and circumscribed. Accor are not going to lose any money on this one. On the other hand, as was my reason from the start for joining, better to be earning something than not. Just not an additional reason to seek them out. (Mine is price and knowing what I'm going to get -- mostly. And the free bus at LHR. Quite enough.)