Just to resolve the arc, I finally went and bought a Kobo Touch today.
I weighed the positives and negatives of the available brands very carefully and finally decided the Kobo ticked the most items on my personal feature wishlist. And I've become dubious from past experience (of both the ereader and PMPs) of the level of support and ongoing development from both the main iRiver company and its distributor here in Australia, so that was a disincentive for buying another iRiver.
Anyway, I recognise these things are personal choices, and that's the one I made. Thanks to everyone on this thread for your observations and suggestions. They were much appreciated. :-)